Lemonaid Wrote:Gun magazines often use as a testing protocol an average of five, five shot groups as an accuracy standard for their evaluation of a gun's accuracy with a brand of ammo. So if I had a load for my rifle that gave sub 1 moa with a load at 100 yard after repeated tests and say it still gets 1 moa at 300 yards will it stay one moa at 1000 yards? (no wind in this thought experiment).
In your hypothetical where there is literally no wind [an underground 1K tunnel?] the stability of the bullet still deteriorates as velocity drops. The Miller stability calculator on JBM [online] demonstrates this. I imagine less stable bullets translate into wider groups. In reality there is always wind and in my experience of 1K F-Class slow bullets can blow out the group dramatically. With 223 as it approached Mach 1 about 900yds the groups would blow out like a cross section of a trumpet. But the other extreme can also blow groups out. Consider an overstabilised bullet resisting pointing down to the target coming out of apogee. As it flies through the air it will yaw.
Now for the tricky part, is the velocity SD baked in the cake so to speak? Good SD, bad SD, in between plus harmonics all combine and don't matter. Is a good SD 1 moa load just as accurate at long range as bad SD 1 moa load?
SD's are not 'fixed', they are simply a single digit reflection of a group of numbers. Change any of the numbers and the SD changes.
Your question regarding the relationship between short and long range is considered because long range is where the velocity of a bullet could have more of an influence on extreme spread (group size) than group size at short range. I had not considered this until it was brought up on this forum. I understand this is also what Satterlee advocates are concerned about and use it as justification for focussing on velocities.
Consider the group as cone of fire that proportionally increases as range does. You allude to this with your 1MOA hypothetical. All things being equal and controlled the best case scenario is going to be 1MOA at 100 is the same all the way to 1MOA at 1,000. We know stability drops with velocity, which has consequences but let's stick to the hypothetical for now.
The group at 100 is made up of rounds with different velocities. Using a ballistic program we can calculate bullet drops for each of those velocities and work out the maximum possible spread by imagining the fastest bullet is at the top of the cone and the slowest at the bottom. If the muzzle velocities are so different that the vertical spread on the target exceeds the 1MOA cone of fire then this becomes a situation where velocities are more influential than group size at 100yd in predicting long range results. In that case velocity SD's can be used as a predictor of max spread at 1K, but are not as definitive as actually working it out.
If we look at those 44 muzzle velocities from the most recent test we get the following for both loads;
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The group size at 100 is extrapolated to 1,000yds (using 1MOA = 1.047inches at 100yds).
The extreme spread of velocities at 100 is also extrapolated to 1,000 using JBM ballistics.
In both loads the group size at 100 has more influence over group size at long range than the velocities. For 21.3gns, the original Satterlee predictor of best load the group at 100yds will translate to a 3.654" group at 1K. The velocity differences of those bullets will translate into a group no bigger than 3.2" at 1K. In this case velocity is a clumsier predictor of 1K group size than actual 100yd group size. This, because the cone of fire will never be tighter down range and as we've discussed will likely be even larger. groups physically cannot contract down range. They always get bigger. But, the velocity prediction of the group at 1K is based on the best possible scenario; the fastest bullet at 12 O'Clock and the slowest at 6 O'Clock. It is more likely then that the velocity groups at 1K will be smaller than predicted.
Using the most recent test the group size at 100 is a more accurate predictor of group size at 1,000, and even more so in reality. This is another nail in the coffin of using velocities to predict results on a target.