ARTICLES FROM CHRIS BEKKER
HOW FAR SHOULD I LOAD FROM THE LANDS?
Since the various bullets offered by Rhino Bullets are all mono-metal bullets (copper and free machining brass), we there for recommend that you start from 2mm (or 79-Thou) from the lands, with a minimum of 1.5mm (or 59-Thou). This allows the bullet to engage the lands (or rifling) with some movement, as the engraving resistance of a mono-metal bullet is generally higher than conventional lead-core bullets.
My recommendation is very much in-line with other bullet makers using mono-metal bullets, such as the Barnes company making TSX bullets. The Barnes Company typical suggests a bullet jump of .050” (or 50-Thou). The distance to the lands (rifling), also called “jump” may be limited by the rifle’s throat length and its magazine length, and to boot, bullet base length to ogive also vary for different types or brands of bullets, and with different ogives shapes (RN bullets vs Spitzer bullets).
Heavy recoil rifles would need a crimping operation to secure the bullet to stay in place, as seated under recoil, preventing the bullet to migrate or move back into the cartridge case. Crimping takes place in the crimping groove just before the start of the ogive. Some long-throated cartridges designs will invariable have longer jumps to the lands, as found in most metric cartridges, such as the 6.5x55, 7x57, 7x64, 9,3x62, etc.
Sometimes the magazine length of the rifle will be the limiting factor, whereby the bullet needs to be seated according to fit the magazine, instead to fit the chamber, as the prime goal is generally getting closer to the lands rather than farther away. Experience of many years dictates that seldom if ever, it is necessary to crimp bullets in cartridges having a lower recoil than a 9,3x62.
In addition, the bullet needs a proper case-neck tension (i.e. grip), which in the first instance is a safety precaution, as well as leading to more consistent pressures and velocities.
- BY CHRIS BEKKER
THE EFFECT OF BULLET WEIGHT VARIATION ON GROUPINGS ON TARGET
In this regard I refer to the booklet of Rheinmetall, titled “Ballistic Data Manual” on Page 26 under the heading “Projectile”, where five (5) physical aspects are being discussed.
1 Grain in bullet weight over 1 000yards makes a difference of 1.5 calibres.
A 1-grain difference:
In .300 calibre (.308”) = @1.5 = .462” at 1 000 yards
= .0462” at 100 yards
= .14” (or 3.5mm) at 300 yards
A 2-grain difference:
A 2 Grain difference in bullet weight creates a double up of the above figures, thus:
.14” x 2 = 0.28” (or 7mm) at 300yards
At practical hunting ranges, the effect is negligible as can be seen as above. Most hunters cannot even shoot a 7mm grouping at 100 yards with factory made rifles.
- BY CHRIS BEKKER
300GR RHINO SOLID SHANK IN A 375 H&H
This is an account of a 375 H&H CZ550 Safari rifle that was loaded with Rhino’s 300 gr Solid Shank bullet… from the bench… to the hunting lodge.
On the bench:
This was done at the shooting range in Johannesburg to zero the rifle for an upcoming hunt.
Once the scope was adjusted to the target’s ‘bull’ we obtained a nice grouping without wasting any further ammunition.
The idea was to let it print an inch high at 100 yards.
300 gr Rhino S/S dugged out from the soil of the backstop.
At the hunting Lodge of Jaco De Wet outside Marble Hall.
Rudi Campbell and myself on a very cold winter’s morning just after sunrise.
The end result: My Blue Wildebeest bull that was standing behind thick brush and trees; affording me only a high-lung shot.
- BY CHRIS BEKKER
SOME ASPECTS THAT WOULD AFFECT THE ACCURACY OF A CARTRIDGE ROUND IN A RIFLE.
For brevity’s sake, I will mention some of the major variables:
A perfectly cut barrel with fine tolerances and uniform grooves - depth & width as no 2 barrels are alike, and in particular, a mass-produced factory barrel with a custom target barrel. There are also different vibration patterns between long and this barrels and short and thick barrels, and anything in between.
A perfectly cut square crown, so the gas blast could exit the barrel in a concentric fashion around the bullet.
Locking lugs that close perfectly square in the recesses of the action.
A chamber that is cut concentric and lined up perfectly with the centre of the bore.
A fine-tuned trigger to release smoothly and lightly.
Ammunition that shows zero runout – a bullet that is seated perfectly.
Using bullets with no inherent ‘bullet imbalance’ – its weight distribution being perfect around its centre axis to avoid wobbling. Bullets may have uneven thickness in the jacket.
Handloading to find the barrel’s sweet spot in terms of barrel oscillations. Typically referred to as finding a ‘node’.
This naturally involves the optimized or correct powder charge for the cartridge, and
Also, the optimized seating depth relative to the rifling of the barrel.
With regards to point number one above:
If you could tune your load so that the bullet leaves the muzzle at a point in the muzzle's vibration where it changes direction (this is called a 'node' in the vibration pattern), it is moving the slowest (and even actually stopping before changing direction), and it is therefore much more forgiving. Tuning your loads to take advantage of these points in the barrel’s harmonics will yield you tighter groups.
As a rule, the thinner and longer a barrel” is, the more it is affected by the vibrations. This is the reason why a "heavy" and thick “match barrel” seems to shoot more consistently than a standard factory “sporter barrel”, and is also easier to tune.
A shorter barrel of the same diameter will have less amplitude to its arc of movement. As you tune the barrel, what you are in effect doing is to change the vibrational length of the free floated forward end of it, causing the vibrational arc, or circular vibrations of the barrel to get smaller and smaller. As the arc gets smaller, the groups are getting tighter. Even though the bullets may still be leaving the muzzle at 12, 4, and 8 O’clock, the diameter of the arc has been lessened, so the triangle gets smaller and the shots start to cut each other.
Then there is the human element of the shooter, that stands separate from the above mechanical parameters.
The bullet’s motion causes a "whipping" motion to the barrel even though your eye is not "quick enough" to see this phenomenon. This is the barrel's harmonic response to the forces imparted on it. Shorter barrels and thicker barrels are affected less than longer barrels and thinner barrels, but they all exhibit this behaviour. We need to recognise this effect on accuracy, being important to those who want to maximize their rifle's accuracy.
By adjusting the seating depth of the bullet, the chamber pressure is changed, as well as the distance that the bullet must travel before it exits the muzzle. These factors will affect the barrel's harmonic response, as well as at what point in the vibration pattern the bullets would leave the barrel.
- BY CHRIS BEKKER
DIFFERENCES IN PRIMERS BETWEEN ‘STANDARD RIFLE’ AND ‘MAGNUM RIFLE’
When the primer ignites the powder in the cartridge, an enormous pressure builds up rapidly, and makes the case expand against the chamber walls to create a seal. This keeps the hot gases from escaping, except by pushing the bullet out of the case mouth and down the bore. At the same time, the base of the case also expands backward and presses against the bolt or also known as the ‘breechface’. What role does the primer play in producing pressure?
A) Ranking of primers – large rifle & small rifle
This table is quite a handy guide or reference to rank some popular primers from ‘hot’ to ‘cool’.
B) A summary of the A-Square test of primers in the Remington 7mm Mag. as published in "Handloader" magazine.
summary of the A-Square test of primers in the Remington 7mm Mag. as published in "Handloader" magazine. This shows why you should always rework a pet load if you switch primer brand or from standard to magnum.
160 grain Sierra boat-tail, 66.0 grains of Hodgdon H-4831 and Winchester cases.
Winchester WLRM (magnum) 3045 fps, 67,600 psi
Winchester WLR (standard) 3024 fps, 64,400 psi
Federal 215 (magnum) 3036 fps, 61,400 psi
CCI 250 (magnum) 3039 fps, 61,500 psi
Remington 9½ M (magnum) 3041 fps, 59,300 psi
CCI 200 (standard) 3011 fps, 54,800 psi
C) Primer pressure differences
Here we can see how the increased pressure is manifesting itself from cartridge case A to C:
C) Primer Testing Reference
I found this on the internet some years ago, but cannot find the source anymore, nevertheless, it was and is quite a good exercise that was done – commendable!
This testing was done to try and rank primers by power (Brisance is the shattering or crushing effect of a sudden release of energy as in an explosion).
Most of the tests were done by 100 or more primers. A few were of 50, when limited amounts were available.
This machine here was a home-made tester.
The shot is fired against a weight, which in turn moves a pointer on the dial.
When the shot is fired, the pointer remains at the highest point of the shot.
Before the shot has been fired:
After the shot has been fired: (In this case a “Federal large rifle magnum”)
Ranked in order of power
Large Rifle = LR, Large Rifle Magnum = LRM, and Match = M
| No | Brand/Type | Power Average | Range | Std. Dev |
| 1 | Fed Match GM215M | 6.12 | 5.23-6.8| .351 |
| 2 | Federal 215 LRM | 5.69 | 5.2-6.5 | .4437 |
| 3 | CCI 250 LRM | 5.66 | 4.5-7.4 | .4832 |
| 4 | Winchester WLRM | 5.45 | 5.1-6.0 | .2046 |
| 5 | Remington 9 1/2 LRM | 5.09 | 3.5-6.75| .6641 |
| 6 | Winchester WLR | 4.80 | 4.1-6.0 | .4300 |
| 7 | Remington 9 1/2 LR | 4.75 | 3.7-6.25| .5679 |
| 8 | Fed Match GM210M | 4.64 | 4.0-5.6 | .3296 |
| 9 | Federal 210 LR | 4.62 | 3.7-5.5 | .3997 |
| 10 | CCI BR2 | 4.37 | 4.0-5.0 | .2460 |
| 11 | CCI 200 LR | 4.28 | 3.8-4.8 | .3218 |
| 12 | KVB 7 LR Russian | 4.27 | 3.8-4.8 | .2213 |
| 13 | Rem 91/2 (30 yrs. old) | 4.16 | 3.8-4.8 | .3427 |
When we make comparisons of anything by way of figures, it is always useful to state the difference in a relative rather than an absolute way – thus in percentage terms. Let us take 3 well known LR primers:
| Primer | Number | Percentage | Description |
| Rem 9 ½ LR | 4.75 | 110.98% | 10.98% more intense |
| Federal 210 LR| 4.62 | 107.94% | 7.94% more intense |
| CCI 200 LR | 4.28 | 100.00% | Base |
And this is why we cannot just swap primers without there being any impact on the load’s performance.
- BY CHRIS BEKKER
THE CAUSES OF PRIMER POCKET EXPANSION
A progression of flattened primers under increasing pressures
Some brands of brass have a reputation for being soft. For example: Winchester brass is much thinner and softer than PMP brass, it can also be seen by the fact that the Winchester case has a smaller internal volume by way of measuring it with water and weighing it. Now add to this a hot load, and more particularly to a high-pressure cartridge. The undue high pressure exacerbates the “abuse” to the brass, and is transferred to the base surrounding the primer cup (web area), deforming the primer pocket ever so slightly, and with repeated hot firings, the pocket grows and becomes loose.
Pockets that expand after a few firings are usually attributed to 3 things - hot loads, soft brass, and an oversize chamber. Sometimes the primer pockets expand after just 2 or 3 firings when the load is not hot, and as we can see no flattening on the primer itself, then it points to an oversized chamber, and that is something you cannot rectify.
Oversized chambers are rare tough, but it happens.
Soft brass can really show loose pockets very quickly after 3 to 4 firings.
Hot loads are quite common, as most people ‘milk’ their cartridges for velocity.
You can imagine the effect when you combine soft brass with a magnum primer and a hot load to boot…. The compounding effect, as it were!
The strongest brass: PMP, Lapua and RWS.
Middle of the road brass: Norma & Nosler Custom Competition.
The weakest brass: Winchester, Remington and Federal.
As of late, Peterson Brass came onto the market, and it is said to be of very high quality – in fact some believe to be the best.
Finally, different brand cases may have different web thicknesses: Below on the left is a Federal .223 case with a thin flash hole web, and on the right is a military Lake City case with a much thicker flash hole web. The thickness of the flash hole web adds strength to the base of the case, and the longevity of the primer pocket. Military brass is invariably thicker than commercial brass.
Below is an exaggerated illustration of the effects of excessive pressure on the base of the case, causing stretching beyond its elastic limits.
- BY CHRIS BEKKER
INTRODUCTION TO PROPELLANTS
HOW DO I CHOOSE WHAT IS RIGHT FOR MY CARTRIDGE
Modern “smokeless” propellants
Since the Somchem booklet does not go into explaining the various types of propellants, and I get continuous questions about loads and propellants for various cartridges, I felt that there was a dire need to provide reloaders with a basic explanation with what we are dealing with. The typical questions that I get are the following:
· Which propellant is right for my cartridge since Somchem lists either 2 or 3 different ones as if it does not matter which one I pick?
· Which propellant is ideal for my cartridge or is there no such thing?
· Is it true that extruded propellants cause more throat erosion?
· Is it true that ball powders are being more temperature sensitive?
· Why must one use Magnum primers with ball propellants?
· How is bullet weight tied to my choice of propellant?
· What are the differences between “Ball” and “Extruded” propellants?
Modern smokeless propellants
Modern smokeless propellants once ignited produce expanding gases that push the bullet down the rifle’s bore, giving it a certain velocity. Propellants have varying burn rates and come in two types for rifles; single base Nitrocellulose and double base Nitrocellulose with the addition of Nitro-glycerine. They have various shapes and they are either extruded or tubular, ball or spherical, round flat flake and diamond flat flake. Contrary to media myths, a smokeless propellant is not an explosive. but rather a highly flammable solid, whereas Black powder is an explosive and a small
quantity ignited even in the open simply explodes. Most smokeless powders are coated with graphite so they will flow through powder measures and funnels. Smokeless powders are also coated with various chemicals to make them more water resistant, to control the burn rate and reduce muzzle flash. Because smokeless powders can deteriorate over time due to the generation of nitric acid small amounts of stabilizers are added to absorb acidic by-products.
Reloading Powder or Propellant
Single-base propellants - Nitrocellulose
Nitrocellulose or "guncotton" is formed by the action of nitric acid on cellulose fibers. It is a highly combustible fibrous material that deflagrates rapidly when heat is applied. It also burns very cleanly, burning almost entirely to gaseous components at high temperatures with little smoke or solid residue. The size and shape of the propellant grains will vary the relative surface area, and so change the burn rate significantly. Additives and coatings can be added to the propellant to further modify the burn rate. A single based propellant has nitrocellulose as its main explosive ingredients. Stabilizers and other additives are used to control the chemical stability and to enhance the propellant’s properties.
Double-base propellants – Nitrocellulose plus Nitro-glycerine
In 1887 Alfred Nobel, a Swede, inventor of dynamite and founder of the Nobel prizes, found that by adding 60% nitrocellulose and 40% Nitro-glycerine, the explosive would serve as a propulsion agent and is called Ballistite also known as Nobel powder (double based propellant). Nitro-glycerine can be added to nitrocellulose to form "double-base propellants". Nitrocellulose desensitizes Nitro-glycerine to prevent detonation, and the Nitro-glycerine gelatinises the nitrocellulose and increases the energy. Double-base powders burn faster than single-base powders of the same shape, though not as cleanly, and the burn rate increases with Nitro-glycerine content.
Short burning times are necessary in short-barrelled firearms, which have only a limited time to transfer energy to the projectile. Double-based propellants also consist of other liquid organic nitrate explosives. Nitroglycerin reduces smoke and increases the energy output. Faster-burning propellants generate higher temperatures and higher pressures; however, they also increase the
wear of the gun barrels. A word of caution: The Nitro-glycerine of double base powder can be absorbed through the skin, by breathing vapours or by ingesting and the symptom thereof may be a headache.
Stabilisers and other Additives
Stabilisers and other additives are also used and added to prevent or slow down self-decomposition or deterioration products. Diphenylamine is one of the most common stabilizers used. De-coppering additives are added to hinder the build-up of copper residues from the gun barrel rifling. Other additives are Graphite and Calcium carbonate. Graphite is a lubricant to cover the grains and prevent them from sticking together, and to dissipate static electricity. Calcium carbonate is used to neutralize acidic decomposition products. Deterrents are used to slow the burning rate.
History of Ball Propellants
"Ball" propellant was produced by a process developed in 1933 by Dr Fred Olsen of Western Cartridge Co, later Olin Chemical, parent company of Winchester, to reprocess obsolete and deteriorating leftover WW I artillery and naval propellants into usable form. They soon went to fresh raw materials. The Nitrocellulose-Nitro-glycerine mix was dissolved and mixed in water to form round globules that become ball-shaped granules when dried and the solvent evaporated. Coatings and rolling the balls more or less flat adjusted the burn rate to what was required.
Cost benefit for the manufacturer
The advantages of ball powder over other types of smokeless powder are many for the manufacturer. It takes a lot less time to manufacture than other types, whereas most other smokeless propellants take a few months to manufacture. DuPont did manage to get one IMR powder type to be manufactured in 2 weeks. In contrast, one production lot of ball propellant could be made in less than two days. Ball powder can also be stored longer than other types. The ball propellant manufacturing process is more efficient in eliminating most of the excess acid, and it doesn't produce much acid as it ages either. The manufacturing process is also safer, as it happens under water and also requires much less specialized equipment to set up a manufacturing line.
Ball powders started to gain popularity in the 1950s. For instance, the ball powder WC 844 is currently used in the NATO 5.56x45 mm. cartridges. So, there are obvious advantages for the military as they can be supplied quicker. All US ball small arms ammunition, some sniper rounds aside, have been exclusively loaded with ball powders throughout the entire 7.62 NATO and 5.56 mm cartridges over the last 60 years. Ball powders were invented to improve the safety of manufacturing, increase manufacturing capacity, and it also reduced the cost by recycling the chemicals used. Hatcher's Notebook has a good write up on the process.
Characteristics – ball vs extruded
· Ball propellants cause less abrasion on the throat area than extruded propellants due to its smaller and smoother geometry.
· Generally, Ball propellants burn hotter and at higher pressure, which is more erosive, but there are exceptions – look at the Heat of Explosion statistics (Kilo-Joules per kilogram). However, peak pressure must also be considered that makes a quick comparison fairly difficult depending on how hot one loads, as the higher the pressure the higher the flame temperature.
· Metering with ball propellant is easier, faster and more precise than with extruded powder and used by Benchrest shooters that do not weigh their charges, saving a lot of time.
· Ball propellants do tend to be more temperature sensitive than extruded ones, but that's only in the extremes for the most part.
· Hodgdon Extreme propellants are known for their stability and are less sensitive than all other propellants to temperature changes.
· Ball propellants need hotter (magnum) primers to burn uniformly.
· Ball propellants foul more - Powder fouling is the result of the combustion of the powder that leaves an ash or residue in the barrel.
· However, if a barrel is cleaned between 20 to 40 shots fouling is basically immaterial.
· Clearly there are differences in ball and extruded, but accuracy is not one of them.
Heat of Explosion (H.O.E.)
Chemical energy is contained within a propellant. The isochoric explosion heat of a propellant is the energy that is liberated by adiabatic combustion of a unit mass of propellant inside a constant volume (adiabatic means that there is no heat exchange with the environment). The temperature reached by the gases during this combustion is called the adiabatic isochoric flame temperature. Combustion gases are hot and flame temperatures run between 3,200°F and 3,400°F (1,760°C and 1871°C), whereas the melting point of steel is around 2,500°F (1,370 °C). High temperatures soften steel and with continued firing it starts to work tiny bits of metal away in the throat area of the barrel. There is a certain relationship between H.O.E. and temperature (they just get measured differently).
· Somchem S321 - 4,010 kJ/kg
· Somchem S341 - 3,660 kJ/kg
· Somchem S335 - 3,710 kJ/kg
· Somchem S365 - 3,685 kJ/kg
· Somchem S385 - 3,680 kJ/kg
Relative Quickness or Burn rate
Relative quickness is the time that a propellant uses to burn up completely. This is done by burning a powder charge in a sealed vessel called a closed bomb and measuring the pressure increase. The closed bomb is filled with powder from 5% to 20% and then ignited and a pressure gauge records the peak pressure. The burn rate, pressure rise, energy content and etc can be figured from this closed bomb test. This information can be used to estimate the way the powder will perform in a particular cartridge and gun. This information is the basis for loads that will be tested in pressure and velocity barrels under controlled conditions, but it is not used as the final charge weight.
Storage of propellants
Propellants should be stored in a cool and dry place. Never expose smokeless powder to direct sunlight. Prolonged exposure to heat above 90°F (32°C) can cause smokeless powder to deteriorate. According to the Hodgdon Powder Company, deteriorating powder usually has a noticeable acidic odour and a red dust or sticky substance may form on the powder. Ignited powder will continue to burn until it is completely consumed. Therefore, propellants must be stored far away from any possible exposure to flames or electrical sparks and other heat sources. Leave smokeless powder in the container in which it was sold.
Many handloaders have discovered that a small variation in powder charge weight usually has little to no effect on accuracy out to the maximum distances they shoot, and for that reason they save time by measuring charges rather than weighing them. Finely granulated propellants meter through any powder measure more accurately than coarser propellants. This is why Benchrest shooters use either ball propellants or fine-grained (SC – Short Cut) extruded propellants made by Hodgdon.
Hodgdon Extreme™ was developed to give shooters consistent performance, load after load, in even the most extreme heat and cold conditions. H4831SC - Ballistically this Extreme Extruded propellant is the exact copy of H4831. Physically, it has a shorter grain size, therefore, the designation SC for short cut. The shorter, more compact kernels allow the powder to flow through the powder measures more smoothly, helping to alleviate the constant cutting of granules. With the smoother flow characteristics comes more uniform charge weights, while the individual grains orientate themselves more compactly, creating better loading density.
More precise and expensive powder measures are being used by Benchrest shooters so they can meter their charges more precisely. I have opted to stay with the term “powder measure” as it is commonly known by most (Americans term) rather than to refer to a propellant measure. One of the most precise powder measures to be found is the Harrell's Premium measure that comes with a longer drop tube to help settle larger powder charges in the case. Measures like the Harrell's have no trouble keeping loads to within tenths of a grain, especially with a ball propellant or very short extruded propellant. It’s a Benchrest quality powder measure and portable so it could be used on the range as well.
Most of us big game hunters and meat hunters load so few rounds of ammunition each year, weighing charges is no big hassle. The standard run of the mill powder measures, such as the RCBS or Lyman, will meter about +/- 1 grain with the extruded propellants and about +/- .05 grain with ball propellants, and then one just has to trickle the balance. High-volume loading is
where a precision powder measure can save a lot of time without weighing each charge. The problem with extruded or stick powders (if we can call it a real problem) is that the powder measure tries to close with a stick half in and half out of the volume cup, resulting in a crunch as the stick gets broken. I've never used a powder measure that doesn't give some level of crunching.
The Powley Equations
Powley's equations are semi-empirical. They use some simplified thermodynamic theory with the numbers altered to fit the results to laboratory data. In internal ballistics, bullet sectional density (SD) plays a vital role. The expanding gasses are pushing on an object (bullet) that has both a mass (mass and weight is the same on earth) and a diameter. SD is expressed as the bullet’s weight in pounds divided by the square of the bullet’s diameter in inches. So, it follows then that for a given bore size it will determine at what rate the bullet will accelerate, or get out of the way. The greater the SD of the bullet, the slower the acceleration will be. Here is a diagram of powder selection by using the Powley Computer, and this was groundbreaking work long before we had computer programs – on the Y-axis we have the bullet’s SD and on the X-axis we have the bore size or caliber if you will:
All internal ballistic software programs exhibit similar results, such as QuickLoad and others, although their mathematical algorithms are private and not in the public domain.
We cannot go by ‘burn rates’ alone
There are far more than 100 types of propellants that span the spectrum of burning rates. Each propellant is manufactured to burn at a specific rate. By varying the granule size, coating, and chemical make-up, these propellants can be made to perform well in the various cartridges that are in use today, but of these 100 or so propellants, from extremely fast-burning to extremely slow-burning, only certain ones will provide optimum results in a specific cartridge. All the others are neither safe nor ideal for a specific application in terms of achieving the best balance of ballistic uniformity, accuracy, and velocity. The multitude of modern propellants is difficult to classify in terms of behaviour. Propellants are ranked in 'burning rate' charts based on a specific test condition in a calorimeter, where its heat and pressure production are measured in a closed and fixed-volume device. However, that is not the real world - in a cartridge case, these rankings may differ for certain cartridges, because of different case capacities and shapes.
Final testing is in a specific cartridge
Furthermore, in the real world, the application brings in another dimension - bore diameter and bullet weight and that is why we cannot just work off a 'burning rate' chart when we need to select an appropriate propellant for a given cartridge. Let me illustrate, a 243 Win and a 308 Win has essentially the same case, save for the fact that bore diameters differ. Through actual laboratory tests, by propellant manufacturers, we know that a 243 cartridge prefers S365, whilst the 308 cartridge prefers a faster burning propellant like S335. Amazing! We cannot now make a deduction that S365 prefers a small bore and light weight bullets, as this propellant is equally adept at giving sterling performance in a 300 H&H with a bigger bore and 200-gr bullets, which is twice the top bullet weight of a 243 Win. Fascinating! Let us continue and shuffle the cards one more time, S365 does not work well in a 458 Lott, whereas it is ideal in a 416 Rigby - clearly the dynamics are different for straight walled cases. Some cartridges though are more forgiving.
It is thus clear why we need ‘lab’ testing, as only there do they consider the operating pressures between 'start' and 'end' loads, which cannot be read off a 'burning rate' chart. From this we can conclude that there are no hard and fast rules, sometimes two or more propellants may work in a given cartridge, but one type from a specific brand may be more ideal. Generally, fast propellants will develop higher peak pressures in a lesser time period, whilst the slower burning propellants peak lower but provide more expanding gasses further down the barrel to yield more velocity in necked-down magnum cartridges, like the various 300 Magnums and some others. In necked-down cases, gas flow is being restricted, which increase pressure, which in turn increase the burning rate of the propellant. That is why the more the case is necked-down, the slower the burn rate of the propellant ought to be. (E.g., the 25-06 Rem prefers the slower burning S385, whilst the 30-06 Spr which is the parent case of the former, performs much better with S365).
General rules for selecting a propellant
As a general rule, the larger the bore, the faster burning the propellant should be, but the capacity of the case and the bullet weight also comes into it. Also, the smaller the case capacity and the lighter the bullet, the faster burning the propellant should be. Generally, ammo manufacturers would look at getting a 100% propellant burn, reaching the desired 'velocity band' at acceptable pressures. Sometimes though, as is the case with the 7.92 mm Mauser (8x57 mm), they download a bit for safety reasons to cater for older and weaker actions that are still in use, so the actions can cope with the pressure.
When bullet weight is reduced in a particular caliber, we effectively reduce the sectional density of the bullet, and so we now need to go to a faster burning propellant bring the operating pressure up again to stay in the ideal operating pressure window for the cartridge. Let me give a practical example: consider that we downscale a traditional load in a 7x57 mm loaded with a 175 gr Hornady RN bullet using S365 by opting to shoot a 130gr monolithic bullet instead. Now we need to change the propellant to the faster burning S335 or S321 and also to get a complete burn to avoid barrel fouling. If we do not do the switch in propellant, pressure will drop and the desired velocity will not be achieved, as that was the main reason for going to the lighter bullet.
Typically, as a general guide, non-magnum loads utilise faster burning propellants, where magnum loads utlilise slower burning powders. Also, for the smaller class of cartridges ball propellants are preferable, because they fill the case better, meter great and provide full power, whereas most extruded type powders are too bulky for best performance in those smaller cartridge cases.
The use of internal ballistic programs and a chronograph
For any given cartridge, there are usually several propellant choices, but one may simply work better. In the past we also had a few cartridges for which we did not have an ideal propellant. A good example was the 416 Remington Magnum that was prone pressure spike in tropical Africa, whilst fine in North America’s colder climate. This temperature sensitivity problem was solved with introduction of IMR 8208 XBR. Unfortunately, we as South Africans do not have access to foreign produced propellants and have to make do with out own. Certain cartridges, such as the 9,3x62 mm with its relatively small case for caliber is often loaded with a compressed load of S365. This is no longer necessary with the introduction of S355, yielding better velocities. A long drop-tube is also handy in gaining better load densities in calibers such as the 458 Win and 458 Lott, as it would obviate having compressed loads at higher end velocities.
Always check a Reload Manual before you start reloading so you know the minimum and maximum loads. So, there are no "cast in stone" rules regarding the selection of a propellant although we have very good pointers from reloading manuals and specific loads that have been pressure tested. QuickLoad is a good source although not perfect, but it can safe you a lot of time and money in picking the most ideal load in terms of optimizing the flowing key parameters:
· Desired velocity
· Within the CIP P-Max pressure range
· A good case fill (90% plus for non-erratic ignition)
· A complete powder burn
Needless to say, that modelling of various scenarios could be done with the program with relative ease that one cannot get from a reload manual. In addition, with modeling one has constantly the “pressure to velocity ratio” in mind as the most important dial in the cockpit. Reloading is much more than just producing ammunition – apart from fine-tuning a load or having the ability to load different types of bullets for your rifle, it is also a journey in internal ballistics that will unfold for you.
One of the most useful tools for any handloader is a chronograph to measure loads with to act as a relative guide how your load combination compares with published loads or the results from a program. Be mindful that when you are changing any component (bullet type, propellant or primer type). It could have a drastic effect on pressure. Thus, always back down on your charges and work your way back up. A chronograph is a valuable tool to assist any reloader; more so than a R8,000 electronic powder measure.
- BY CHRIS BEKKER
BULLET CONSTRUCTION – HOW IMPORTANT FOR BIG GAME LIKE BUFFALO.
In soft expanding bullets, I regard the construction of the bullet as important in terms of its weight retention ratio, but it should also be in conjunction with controlled expansion. A higher weight retention ratio helps to preserve as much momentum as possible to drive the bullet forward on its journey, because the expansion of the tip would inhibit penetration, or to put it differently, expansion of the bullet’s frontal would be working against the driving force (mass x velocity). One could also say that the expansion of the bullet is fighting against mass that was put into motion.
Expansion is important, as that is the very purpose of having a controlled expansion bullet, as we want to create a larger wound channel through the vitals of the game that we hunt. The ideal expansion is somewhere between 2 and about 2.3 times of original diameter. Some thin jacketed bonded bullets open up to more than 2.5 times, and sometimes up to 3.2 times, and that inhibits deep penetration, mainly because the construction of the bullet is such that the expansion is not arrested at some point, and so higher impact velocities which are exceeding the threshold strength of the bullet, will invariably result in a too broad frontal area and encounter more drag with the result that one could have shallow penetration. Some bonded bullets do not have a mechanism to arrest expansion. The Swift A-Frame bullet has a cross member to stop expansion at some point, whilst it does have a bonded front lead core. The Rhino Solid Shank bullet has a solid shank of copper and a bonded lead core in front that opens up a bit wider than the Swift A-Frame.
Factors influencing bullet performance:
a) Velocity ...either too low (poor penetration) or too high (bullet failure)
b) Distance ... impact velocity should be in line with the target's distance.
c) Weight and toughness of the animal ... thin-skinned, thick-skinned or dangerous animal?
d) Construction of bullet ... conventional, partition, core bonded, solid shank or monolithic a hollow point?
e) Properties of the bullet ... sectional density, form and hardness of metals.
Thus, we need to recognize that all the above factors work in harmony (in conjunction) to produce a terminal result. The Rhino bullet, is not only making our rifles more effective, but it is also changing our views on terminal ballistics. By gaining say 35% or more 'after impact' bullet weight, avoiding bullet fragmentation, the formation of a bigger mushroom to cause a wider wound channel, and the retaining more mass and momentum to smash heavy bones.
The motto being… "Rather spend an extra buck on a bullet, than an extra bullet on a buck".
Here is a comparison of the Swift A-Frame and a Rhino Solid Shank Bullet retrieved from buffalo; both shot with a 500 Jeffery – notice the difference in the size of the expansion:
Swift vs Rhino – Top View:
Swift vs Rhino – Rear View:
There are some other expanding mono-metal bullets available that do not open wide enough, because the hole that is drilled in front of the bullet is too shallow, and thus it cannot open up wide. In other instances, a bullet might open up fully at within a given distance range based on its operating velocity window, but once the velocity drops too low, the bullet will not open up fully as intended. This is why one should be aware of the fact that in most controlled expansion bullets, one should not drop below around 2,000 fps striking velocity, bearing in mind that bullets do differ in this regard as to their strength.
Since we talk about wat we consider a bullet’s ideal construction, I prefer a bullet that opens up with 4 petals of equal size, as that helps the process of opening up in a concentric way, so as to keep the bullet progressing in a straight line. In this regard, I wish to mention that the Rhino Solid Shank bullet and the Barnes TSX bullet, is guided to open up in 4 equal petals, allowing some of the crushed tissue to move between these petals.
Here you can see an example of a .375/380 gr Rhino Solid Shank bullet that exhibits the features that I highlighted
TESTING OF SOME 7MM BULLETS
This is an array of 7-mm bullets that I fired in my 7 x 57 mm rifle into a wetpack at 25 yards. The above picture tells the story of the 4 bullets that I tested.
1) Far left - As most of the time you can expect sterling performance from a Barnes-X bullet - no weight loss and a perfect mushroom. You can clearly notice how its petals that are thinning towards the front are spiraled by the induced twist, showing the twist-force present on impact. In fact, one can see the twisting better on the Barnes-X bullet than on conventional lead-core bullets or the thick-jacketed Rhino Solid Shank bullet. How ever 'insignificant the "4/10ths of a percent" of the forward energy the twist might be, but you cannot bend those petals back by hand, even when using a pair of pliers.
For those damning critics that say the 7 x 57 mm is just a “lady’s gun”, consider this…. let me enlighten you; a 175-gr Barnes-X bullet out-penetrates a 286-gr 9.3 mm bond-core bullet (bigger mushroom).
2) Second from left - The Nosler Partition bullet, designed in 1946, will almost always lose its front core; disintegrating in the target. The thin petals fold back close to the shank and invariably pieces of the jacket are being torn off. The rear core is protected by a cross-member and provides retained weight (approx. 65%) to ensure acceptable penetration in most cases, but it’s a compromise hunting bullet in my humble opinion when compared to more strongly constructed bullets of today.
3) Third from left - The Claw bond-core bullet, another locally made South African bullet, made from 1-mm copper tubing. At 7 x 57 mm velocities, its weight retention is good (99.4%) and it forms a nice big mushroom - a nice hunting bullet at a very economical price. I have not checked this bullet out at higher 7 mm Rem Mag velocities, but expect some deterioration of over-expansion at higher impact velocities.
4) Far right - The Sierra Game King bullet - a misnomer in my humble opinion, as it is everything but a bullet intended for game, and definitely not to a king’s taste. The lead-core disappeared and disintegrated completely; all I could find was this peace of jacket weighing a mere 28.5%.
Penetration was shallow, only 3.5 inches, as it lost most of its weight, and thus its momentum (the driving force) on impact. Again, the bullet’s thin petals just folded back close to the shank – not ideal in my opinion. It begs the question, what would happen at 7 mm Rem Mag velocities?
Well, there you have it in a nutshell, and this is exactly what you can expect in game, and in some cases even worse when you encounter bone. Pick your hunting bullets wisely and start to reload, if you don't do it already.
THE CASE FOR THE CONTROLLED EXPANSION BULLET
Today discernible hunters opt for premium grade bullets
Not all bond-core bullets are created equal - some have thin jackets and others have thicker jackets, meaning that the thin-jackets would fold their petals close to its shank very quickly, which is far less desirable in my opinion, relative to a bullet that keeps its petals wider to create a bigger wound channel, and these thin-jacketed and non-bonded bullets do lose more weight. Also jacket material varies from pure copper to harder and more brittle gilding metal (Cu 90%/Zn 10%).
Molecular bonding of the lead core with the copper jacket produces much better terminal performance in hunting bullets, provided they don't over expand to inhibit deeper penetration. The cure is to arrest expansion at some point to ensure that the expansion is stopped somewhere between double diameter size and about 2.5 times at maximum of original diameter. To limit expansion, it has to be arrested at some point either with a partition or a solid shank, and in addition, to experiment with the bullet’s jacket thickness in the ogive section.
Some bullet makers let the wall thickness taper towards the nose to aid expansion during the initial stages, whilst some other also cut grooves at the tip or serrate the jacket to force the bullet into 4 even petals; the size of the exposed lead tip being critical to initiate expansion. This ensures controlled expansion, as well as deeper penetration than what we get from conventional lead-core bullets that either shatter or over-expand. The controlled expansion bullet design extends the velocity window of hunting bullets as they have a higher threshold strength to protect the integrity of the bullet. I consider the ‘solid shank design’ to be superior over all other designs.
A 286 gr 9.3mm bullet retrieved from a Hippo -21.5 mm expansion
Bullet construction, expansion and penetration potential
Premium grade bullets distinguish themselves from traditional cup and core bullets (a.k.a. conventional bullets) essentially by offering a much stronger construction to deal with the rigours of higher impact velocities. Some features of controlled expansion bullets are:
· Expansion must be arrested at some point to avoid over expansion and thus shallow penetration
· High bullet weight retention aids momentum to drive penetration
· Concentric expansion of petals makes for straight-line penetration
· Dart stabilisation is achieved when the bullet’s centre of mass shifts forward
A bullet’s expansion tendency will greatly influence its ability to penetrate, as it boils down to momentum (force) over the bullet’s frontal area. Simultaneous with this, bullet weight loss interacts in a dynamic way to reduce the bullet’s momentum in the terminal phase (meaning at range when its velocity has dropped off, and after it has shed some weight on impact). Even if a high weight retention ratio is achieved, we see that the over expansion of the frontal area inhibits deep penetration.
Expansion of more than 2.5 times original diameter is not ideal in my opinion, unless more momentum is brought to bear to drive deeper penetration. I regard in general an expansion as ideal and more than adequate between 2.0 and 2.3 times, which is wide enough in all calibers that we hunt game with, and penetration is not unduly compromised. Likewise, I do not like hunting bullets that make a small “mushrooms”, shed a lot of weight, and losing its petals before it goes through the vital organs.
Not even to mention the fact that bullets that shatter and a make a mess of the meat, even though dramatic and spectacle kills can be achieved with ‘behind the should shots’ on soft-skin game, where the lungs explode as the bullet shatters in thousand pieces of lead particles. The connoisseur meat hunter has better choices today than the frangible bullets of yesterday.
HOW IMPORTANT IS THE BC OF A BULLET FOR A HUNTER?
BC’s need to be balanced against practical hunting ranges
The Ballistic Coefficient (BC) of a bullet is basically just an index number that is used to describe a bullet’s aerodynamic drag relative to a reference standard. While bullet manufacturers commonly include BCs in their product descriptions, often times those numbers are merely a mathematical calculation, rather than the result of actual test firing. Also, since the true drag profile of a bullet changes over the course of its trajectory, using a single BC is just an approximate way to predict how a bullet will actually perform over a long distance, but naturally less so over shorter ranges.
G1 versus G7
Be that as it may, we have essentially two drag functions, namely G1 and G7 that are used for commercial bullets, which are used in ballistic software programs. G1 is the drag function for a slightly modified standard bullet shape, and G7 is the drag function for long, slender bullets with boat-tails, the so-called very low drag bullets (VLD). G1 is used by most bullet manufacturers, while makers of very low drag type of bullets are recommending the use of G7.
G1 and G7 both refer to aerodynamic drag models based on particular “standard projectile” shapes. The G1 shape looks like a flat-based bullet, whereas the G7 shape is quite different, and better approximates the geometry of a modern long-range bullet. So, when choosing your drag model, G1 is preferable for flat-based bullets, while G7 is ordinarily a “better fit” for longer, boat-tailed bullets
Use of ballistics tables or ballistics software programs based on the Mayevski/Siacci method and the G1 drag model, introduced in 1881, are the most common method used to work with external ballistics. Projectiles are described by a ballistic coefficient, or BC for short, which combines the air resistance of the bullet shape (the drag coefficient) and its sectional density (a function of mass and bullet diameter) – commonly given by the formula of the bullet’s sectional density divided by its form factor. The form factor was a number that accounted for the different shape of the non-standard bullet compared to the standard bullet.
G1 shape of the standard projectile
The BC value for the standard bullet then is 1.0 (weight 1.0 lb., diameter 1.0 inch, and form factor 1.0 by definition for the standard bullet). The physical unit of the BC are pounds per square inch (lb./in2). BC values for hunting bullets with a value higher than .400 are considered to be high, whereas for target shooting it is more like .500 and above.
We have several different drag curve models optimized for several standard projectile shapes, and are referred to as follows:-
· G1 or Ingalls (by far the most popular)
· G2 (Aberdeen J projectile) · G5 (short 7.5° boat-tail, 6.19 calibers long tangent ogive) · G6 (flatbase, 6 calibers long secant ogive)
· G7 (long 7.5° boat-tail, 10 calibers tangent ogive, preferred by some manufacturers for very-low-drag bullets)
· G8 (flatbase, 10 calibers long secant ogive)
· GL (blunt lead nose)
The G1 BC drag curve gets its name from the standard projectile fired by the Gàvre Commission of the French Naval Artillery, which was convened between 1873 and 1898. The Ingalls tables, however, were derived from Russian General Mayevski's analysis of firings done by the Krupp factory at the Meppen Proving Grounds in Germany between 1875 and 1881, and which got up to 3,000 fps.
The projectiles used by the French, Germans, Russians (Mayevski had done his own firing tests between 1868 and 1869, but the maximum velocity was only up to 1,340 fps), and English (Francis Bashforth, inventor of the Bashforth ballistic chronometer, who conducted extensive firings between 1865 and 1880), were all similar. They were flat base projectiles with 1.5 to 2 caliber radius tangent
ogives followed by around 1.8-2.5 calibers of straight sides, interrupted by artillery shell rifling engraving bands. The result is that if you look at graph of the drag (rate of velocity loss) data points at different velocities, you get a very similarly shaped curve for all this old data. That is why Ingalls tables and G1-based projections don't disagree by much. Keep in mind that the folks in the 1880's were not so advanced in modern physics as today. The first attempts to solve the differential equations of aerodynamic fluid flow didn't come about until the 1930's. The tables and formulas used to describe the drag functions based on the early data were therefore curve-fitting exercises, and not formulae attempting to calculate drag from first principles. Doppler radar-measurements For the precise establishment of drag or air resistance effects on bullets we need to do Doppler radar-measurements on each type of bullet, which will be unique to that bullet shape. With the help of Doppler radar-measurements bullet specific drag models can be established that are most useful when shooting is conducted at extended ranges where the bullet speed slows down to the transonic speed region near the speed of sound. This is where the bullet’s drag profile predicted by mathematic modeling can significantly depart from the actual drag experienced by the bullet. Some commercial companies are going this way now.
Other factors affecting BC’s
Technically drag models applies only to a particular bullet, so using them to predict another bullet’s performance is an approximation, but the results can be very close if the proper drag model is used. The G1 model provides results close enough to the actual performance of most commercial bullets at moderate ranges (under about 500 yards) that it is commonly used for all commercial ballistics computation. Note that there are two standard sets of meteorological conditions in common use. The older one is known as Standard Metro or Army Standard and the more modern is called the International Civil Aviation Organization (ICAO) standard. The characteristics of these two standards are listed below.
While they are similar, the different parameters do have a slight effect on calculations and in effect change the standard atmospheric density by about 1.8 percent. Under ICAO conditions the speed of sound is 1,116.5 fps and under Standard Metro conditions it is 1,120.27 fps. Since a quoted ballistic coefficient depends on atmospheric density, the same bullet has two different BCs depending on the conditions used. If a quoted BC based upon the Standard Metro conditions is used in a ballistics program based upon the ICAO standard, the BC needs to be modified by multiplying it by .982.
Standard Metro ICAO
Altitude Sea level (0′) Sea level (0′)
Temperature 59° F 59° F
Barometric Pressure 29.5275″ Hg 29.9213″ Hg
Humidity 78% 0%
Conversely, ICAO based BCs need to be multiplied by 1.018. While this is a very small change and has little effect at short range (under 500 yards), it does have an effect at longer ranges. Needless to emphasize that atmospheric conditions can play a role when extremely large differences are encountered in terms of air density, which depends again on altitude, temperature and humidity.
Match bullets used in target shooting
Bullets designed for supersonic use (like in Palma and F-Class) will invariably have a slightly tapered base at the rear, called a boat-tail, which reduces air resistance in flight. Cannelures, or crimping grooves, which are recessed rings around the projectile to crimp the bullets securely into the case, will cause an increase in drag, and so you will not see it on match bullets. Crimping grooves are intended for larger more powerful rounds so as to secure the bullet from slipping due to high recoil – generally from .375 H&H up.
The effect of differing BC's, but the same velocity. (180 gr .308” Speer Bullets)
I modelled a typical .308 Winchester PMP load with a heavy bullet at modest velocity to get the worst trajectory possible from this cartridge. It is good to see a worst case scenario.
This table gives us an appreciation of the effect of BC on its own, as we keep velocity static. Clearly a Spitzer bullet is better suited for long range work, whilst the Round Nose bullet is meant for shorter range work. However the differences above at 200 yards are negligible. The effect of BC really starts to kick in from 250 yards and beyond, if one zeroes at 100 yards. However if one zeroes at 200 yards or at the MPBR, the scenario changes to be even more accommodative of bullet drop, and so lessens the importance of BC for the hunter.
So, generally speaking Round Nose bullets are for shorter ranges as they encounter more air resistance, Semi-Spitzers are more suited as mid-range hunting bullets. I have assumed a wind factor of 10 miles per hour in all tables that I modelled. As can be seen the bullet drop of the 3 bullet shapes are totally insignificant at 200 yards, and even at 300 yards we can live with the marginal differences on game the size of kudu when we go for the vitals (heart & lung area) as opposed for head shots.
How a 300 Win Mag performs at long-range hunting.
· I decided to model a 180 gr Barnes-X bullet.
· BC = .450
· Case fill = 90%
· Charge = 67.4 gr of S365
· Velocity = 2,900 fps
· Pressure = 56,180 psi
· Bullet prints 2.5” high at 100 yds
As a rule of thumb when you zero at a particular distance, in this case at 250 yards, you are good to go for a further 50 yards at a drop of 3.7 inches that one can comfortable live with. However, push it another 100 yards from the zero distance, and you have to compensate and it puts you fair and square at risk with a 9.1 inches drop. Since most hunting is done below 300 yards, we can conclude that we do not have to rely on BC so much, but rather on correct range estimation, and know at what distance to zero for the terrain.
Big Bore Cartridges
BC’s are actually of no consequence in big bores cartridges, like in .375 H&H; .404 Jeff; and in .458 Win Mag. These rounds are used most of the time within150 yards, accepting that some hunters want to use their .375 H&H at longer ranges, making it a more versatile round. And so, when zeroed at 100 yards, one can ignore bullet drop rates for these cartridges out to 150 yards.
Here is another study that was done, and I quote…. "Ballistics expert Keith Luckhurst ran some trajectory tests comparing a .404 Jeffery loaded with 400-grain bullets at 2,280 fps, a .458 Winchester Magnum loaded with 500-grain bullets at 2,090 fps, and a .375 H&H leaded with 300-grain bullets at 2,550 fps, all sighted in at 100 meters. According to Luckhurst, “At 250 meters the .375 Magnum has dropped 11 inches, the .404 has dropped 13 inches and the .458 has dropped 18 inches. But at 150 meters there is a spread of only one inch between these calibers, and at 200 meters it is four inches. Most gun writers would describe the .375 Magnum as flat shooting and the descriptions of the .458 tend to include words like ‘rainbow trajectory.’ In reality, the point of aim for any of the rifles is virtually the same out to 150 meters.” Luckhurst concludes that the .404 Jeffery, with better penetration and less recoil than the .458, a trajectory almost as flat as the .375 H&H, and overall performance similar or equal to the .416 Rigby, is a particularly well-balanced rifle for the largest and most dangerous game."
Small Bore Cartridges
With small bores such as 7x57mm; .308 Win; 30-06 Spr & .300 Win Mag, it is best to revert to a Maximum Point Blank Range (MPBR) method. For this you need computer modelling though to give you all the break points. A maximum MPBR varies depending on your target size in terms of the radius of the vital zone. For a kudu, all you have to do is be able to put a round into an 18" circle, but to be conservative you could reduce it to say 10” for more precise shooting. Thus we model on a 5” radius to determine our maximum range. Using a theoretical bull’s-eye (the centre of the vitals) you can have your round strike 5" high to 5" low, and still drop the animal within less than 50 yards or so.
For example: Using the very same load (180 gr Barnes X Solid base @ 2,900 fps) as above in the .300 Win Mag, sighting it in on the MPBR method at 298 yards, picking a 5” vital radius, it will print 4” high at 100 yards, 4.7” high at 200 yards, -0.2” at 300 yards, -5” at 350 yards and -11.7” at 400 yards. That allows for the entire path of travel for the bullet to never exceed 5" above the line of sight, and drop 5” below the line of sight, which is the capability of your rifle; giving us the maximum point blank range. You simply hold dead on and pull the trigger; No need for any compensation. And so the zero range is actually far more important than relying on a bullet’s higher BC to yield a flatter trajectory, as it affords you only a marginal benefit at practical ranges, and much less than getting you zero range or MPBR correct.
Swarovski’s Ballistic Turret - The ballistic turret gives the hunter the means to set a zero distance plus 3 more easy to set zeros – thus 4 clearly marked settings.
The only other way, which is more accurate, is to buy yourself a “dial-in” scope like a Swarovski Z5, and zero your rifle at 4 different settings at say 100; 200; 300 and 400 yds. With this method you range the distance of the animal with a rangefinder, and simply move the zero clicks up to the required setting in an instant, and you are ready to pull the trigger. Nothing beats this method for accurate shooting.
MORE COMING SOON...
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