Last time I was getting one flier in every group with the 180GC, and one guess was that the flier might be caused by the bullet self-seating deeper into the neck when chambered. There was definitely a lot of variation in effort required to close the bolt. Neck tension was only 0.002" or less, so I decided to try more neck tension, with the hope that the bullet would engrave as the bolt closed, rather than self-seating. So I converted my homemade case sizing die to a bushing-style die, with a 0.323" neck bushing. That increased neck tension from 0.002" to 0.008".
Naturally I forgot to take a picture of the converted die -- maybe in the next few days.
All of the loads shot today were loaded with the 0.323" neck die.
Counting from left to right:
Row 1, Column 1: the same IMR8208 load that I shot last week, except now with more neck tension. The neck tension seemed to improve velocity variation, and bolt closing effort was very consistent. Accuracy was no better than last week, though.
Row 1, Column 2: same load as column #1 except all the grooves were filled with lube. Accuracy improved but velocity variation doubled, go figure. The rest of today's loads also used lube in all grooves, since it seemed to improve accuracy.
Row 1, Column 3: same load as column #2 except bullet final sized to 0.3095" instead of 0.3085". It did not help and may have hurt so I went back to 0.3085" for the remainder of today's loads.
Row 1, Column 4: LT32. Nothing exciting.
Row 1, Column 5: LT30. It lost 4 gas checks out of 10 shots fired. 3 of those shots went into the group while the 4th was the low flier. None of the other loads have lost a gas check in this barrel, so that is an interesting clue. Maybe the violent acceleration of the faster powder has something to do with it?
Row 2, Column 1: N133. Not bad, though no better than IMR8208.
Row 2, Column 2: RL15. The best velocity variation so far, and a pretty group.
Row 2, Column 3: H4895. The 2nd best velocity variation so far and a respectable group.
Showing how the bullet is sized and seated Ardito-style. It looks funny with the big bullet sticking out of the puny case. Preliminary Conclusions:
-- 0.008" neck tension may have reduced velocity variation, and did not seem to hurt anything.
-- filling all the lube grooves seems to improve accuracy but hurt velocity variation.
-- 0.3085" final size diameter seems to work best.
-- LT30 seems to kill gas checks
-- RL15 gave the best velocity variation to date.
-- try IMR4166, WC844, WW748, WW760, WC845, and Leverevolution.
-- a lot of CBA competitors use N135, but I don't have any on hand.
-- After settling on a powder, experiment with more bullet designs?