The following are the findings from shooting up to 100 shot groups, as per the following Hornady YouTube videos:
Taking these learnings here is a suggested approach for working up a load for ELR (Extreme Long Range):
- Seat your projectiles to a 25-30 thou jump and forget your seating die is adjustable
- For a given projectile load up 10 rounds for each suitable powder you can find
- Shoot a 10 shot group for each powder and look for promising candidates
- Explore those promising candidates with more 10 shot groups
- Use computer software such as OnTarget to calculate mean radius, and to combine targets together (shot in the same environmental conditions) to form 20 shot composite groups for your given projectile/powder combination
- If none of the powders look promising change your projectile, don’t faff around with powder charge weight or bullet jump
- When you’ve settled on a projectile/powder combination that works in your rifle system set your zero angle using a 10 or 20 shot composite group
Explain this crazy talk!
- Small sample sizes (3 and 5 shot groups), can sometimes tell you how bad something is, but can never tell you how good something is. They cannot be relied upon to give you accurate dispersion, velocity, or zero information.
- OCW (Optimal Charge Weight) and Velocity flat spots are mirages which are not repeatable and disappear when you fire 30/50/100 shots at each powder charge weight.
- Large changes in dispersion can be found by changing projectile/powder combinations
- Small changes in dispersion can be found by fiddling with powder charge weight and jump distance
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The higher the powder charge, the higher the velocity, the marginally higher the dispersion
- Standard Deviation figures can only be relied upon as a predictive tool if your sample size is big enough to form a normal distribution. Anything less than 30 shots in your sample, you do not have a normal distribution and your SD’s are not useful as a predictive tool.
How variable is my dispersion for different samples sizes smarty pants?
As you increase sample size you funnel your dispersion values into a tighter and tighter band. At some point you will reach a tight enough band to satisfy your expectations.
For example in this rifle system, 5 shot groups vary in size from 0.20 to 1.40 inches, all factors remaining the same. Every gun will pull off a 5 shot quarter minute group if you shoot enough groups, but if you want to know what your system can consistently do, you need to shoot larger groups.
How far off is my rifle’s zero?
If you zero with a 3 shot group, it can be a couple of clicks off in any direction. At extreme long range, this zero error will lead to target misses. A 10 shot group will get you closer, a 20 shot group closer still.
Those busterds just want me to buy more Hornady bullets!
Of course they do.
No one wants to shoot 30 shot groups for every change in a variable. It’s not viable for many reasons including affordability, burning barrels etc.
However hopefully what they have learned, and shared, by burning up tens of thousands of rounds is give you the data you need to come up with a strategy for working up a good handload for your own ELR rifle system, with a good zero angle, to avoid making costly assumptions and adjustments with 3 and 5 shot groups.