Читать книгу Marksmanship Fundamentals - Pseudonym Sniper - Страница 7

Ammunition is a major factor because even if you do everything else right, if your ammo isn’t fit for purpose then you will never achieve the level of accuracy and precision you are striving for.

You also need to think about your intended use.

Applied Ballistics Munitions (ABM), produce ammunition that rivals hand-loaded ammunition for consistency.

For example if you are shooting in competitions such as F Class, you will want to use match/target projectiles which have excellent external ballistic characteristics. The downside is that these projectiles usually have poor terminal ballistic characteristics so are not ideally suited for hunting.

By contrast, if you are hunting, you will want a projectile that has good terminal ballistic characteristics. The issue is that you usually have to compromise somewhat on the external ballistic characteristics, however the impact isn’t significant because with hunting, you are generally targeting a large area (i.e. a 10” target area on a deer at 1000y vs. 5” Bull in F Class).

When it comes to ammunition, you want a projectile with a high BC (Ballistic Co-Efficient), and if you plan to shoot extended long range (i.e. through the Transonic and Subsonic flight zones) a projectile that maintains good stability as it travels through those zones.

You also want your ammunition to yield a suitable MV (Muzzle Velocity).

What do I mean by suitable?

Well, an MV is suitable if the ammunition can do what it is designed to do.

For example, wind is a huge factor when shooting long range. A projectile travelling at a lower speed/velocity is influenced to a greater degree than a projectile travelling at a higher speed. Therefore, the higher the MV, the less effect wind has on your projectile.

Likewise, if you are hunting, most hunting ammunition is designed to cause extensive damage when it strikes the animal (when it strikes within a certain velocity range) to ensure a quick and humane kill/incapacitation.

If the MV is too low, it reduces the range at which you can engage an animal because the ability for the ammunition to cause the necessary amount of damage is reduced due to the lower velocity.

Hand in hand with a having a good MV is having a low and consistent SD (Standard Deviation).

For the benefit of those that don’t know, SD is the “average” variance in MV as measured by a Chronograph.

For example, if you shoot a 20 round string through a Chronograph you will generally get a High MV result, a Low MV result, and an Average MV result.

The High MV result is the speed (velocity) of the fastest round recorded. Let’s say it was 2620fps.

The Low MV result is the speed of the slowest round recorded. Let’s say it was 2580fps.

The Average MV result is the average speed of all 20 of the recorded shots.

The SD is the “average” speed deviation of the rounds above or below the Average MV over the 20 shot string.

So…an SD of 10fps means that the average deviation in MV between the 20 rounds fired averages +/- 10fps.

Now…just to clarify…just because the “average” is 10fps it doesn’t mean that all rounds will be +/- 10fps or less. What it means is that around 68% of your rounds will be within this range.

The benefit of having a low SD (10fps or less) is that at long range, the lower your SD, the less vertical dispersion you have between your rounds.

So…let’s say your average MV is 2649fps and your SD is +/- 10fps. That means that at 1000y, a round that is travelling 10fps faster (2659fps) will strike 7.2” high and a round travelling 10fps slower (2639fps) will strike 3.6” low.

I hope this helps give you an understanding. Now…moving on.

With factory match grade ammunition or Military Sniper ammunition, you should be able to achieve an SD of 15fps or lower (as measured by a Chronograph), which is acceptable.

If you are shooting in competition, you want the SD (Standard Deviation) of your rounds to be around 10fps or lower but to achieve this it usually requires you to use reloaded/hand-loaded ammunition.

However, there are a few manufacturers that can produce 10fps or lower ammunition, Applied Ballistics is one example.

The benefit of using the Applied Ballistics ammunition is that their “Berger” projectiles generally work pretty well as hunting projectiles also (unlike most other manufacturers).

As with everything in Long Range shooting, consistency is key. Up next we have the rifle…