I am reloading for a 7mm WSM
in a Mod 70 Win Coyote, it still has the original chambering and about 1400 rounds through it. I am using a Redding bushing die. Not to long ago I discarded a bunch of brass because the bullets slipped inside the mouth after using the same bushing (.312) as I always used. I concluded that I may have turned the necks to much, since I am new at this.
So I bought 100 more Win cases and started over. No neck turning at all, and using the .312 bushing. I loaded several dummy rounds in the new case and they consistantly measured .313 so I thought I was good to go with the .312.
I fired several sessions with no problem encounterd. My reloads that I used is not really hot, 69.5 H1000 and the 162 AMAX. 3/4 MOA @ 100 most of the time. However, after the third firing and subsequent resizing using the .312 bushing, the same problem came back. The case lengths are in specs. I used a .311 bushing for a few firings and I'm getting loose necks again. Not all the cases are doing this but at least half of them are. Primers are fitting good, case neck and bullet runouts are as consistant as before if I'm reading my RCBS case gauge correctly, as are the neck thickness measurements. But It isn't an accuracy problem.
Should I go down to a .310 bushing? Am I doing something stupid or is.003 under where I need to be? The fired brass measure .320, the loaded is at .313. I've annealed the cases.
Any thoughts on this would be a great help.