I got a couple of new barrels, both 6.5, and I was getting poor groups. I had measured the cases to check water capacity, before shooting them. I repeated the water capacity test after firing (the first cases were resized from new .243 Win cases [Win brand], and necked up to .260 Rem), and the second string of weights was 1.75 gr higher than the first, resulting in a calculated powder charge error of about 0.9 gr, per the Optimal Barrel Time node combined with QuickLoad calculation. The Win brass is about as consistent as any, compared to Lake City and Lapua. (I did a test of water capacity and consistency on LC and Lapua with 60 cases of each awhile back.) The groups tightened up nicely (10-shot group of 0.73"), and I put that rifle away to work on the 6.5 Creedmoor. I have been loading 6.5 CM with Hornady cases. They have good capacity, 53.5 gr on initial testing; but since I was looking at these new barrels, and these are also new calibers for me, I repeated the capacity test on the Hornady cases. The capacity did not change, but the range of capacity was 1.3 gr. That does not inspire confidence, so I sized some Lake City brass down to 6.5 CM. The initial weight capacity was 50.8 gr of water. I calculated a load per OBT/QL, and shot 10 shots. I started with a cold-bore, which was out of the group, then shot the next 9 into 0.46", with the 10th sh
ot (called good) out of the group, making the 10-shot total 0.79". I weighed the cases again, and came up with the same water capacity, 50.8 gr, and a 0.7 gr range of capacity, just as with Lake City in .308, and Lapua. The distribution of weights demonstrated a good bell-shaped curve. The same group size test using the Hornady cases resulted in a group of 0.9" for 10 shots (a fairly round group). This is only one test, and a fairly small sample size, but this appears to be statistically significant. The shots from the resized LC brass which were out of the group were due to vertical. The 0.46" measurement was almost all horizontal, with a vertical spread of 0.31" on the 9 shots in the middle hole. I plan to repeat the water capacity on some newer Hornady cases, since the ones with the large variation were from different boxes of once-fired factory-loaded ammo. They are very good cases (loaded ammo run-out has never been over 0.001"), but until I verify consistent capacity, I won't use them at long range or in competition. Well, I don't compete any more; but I still like to know what works and why.
Mea culpa (edit). One fact needs clarified: the 0.93" group with Hornady cases was a 20-shot group, which was 0.80" without the cold-bore shot. I need to repeat the shooting part of the test with LC and Hornady cases, and shoot 20 shot groups, to be comparing correctly. I'll only re-post if there is a change in the results. Also, the range of water capacity for the Hornady 6.5 CM cases was actually 1.5 gr.
ot (called good) out of the group, making the 10-shot total 0.79". I weighed the cases again, and came up with the same water capacity, 50.8 gr, and a 0.7 gr range of capacity, just as with Lake City in .308, and Lapua. The distribution of weights demonstrated a good bell-shaped curve. The same group size test using the Hornady cases resulted in a group of 0.9" for 10 shots (a fairly round group). This is only one test, and a fairly small sample size, but this appears to be statistically significant. The shots from the resized LC brass which were out of the group were due to vertical. The 0.46" measurement was almost all horizontal, with a vertical spread of 0.31" on the 9 shots in the middle hole. I plan to repeat the water capacity on some newer Hornady cases, since the ones with the large variation were from different boxes of once-fired factory-loaded ammo. They are very good cases (loaded ammo run-out has never been over 0.001"), but until I verify consistent capacity, I won't use them at long range or in competition. Well, I don't compete any more; but I still like to know what works and why.
Mea culpa (edit). One fact needs clarified: the 0.93" group with Hornady cases was a 20-shot group, which was 0.80" without the cold-bore shot. I need to repeat the shooting part of the test with LC and Hornady cases, and shoot 20 shot groups, to be comparing correctly. I'll only re-post if there is a change in the results. Also, the range of water capacity for the Hornady 6.5 CM cases was actually 1.5 gr.
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