Some of you (esp those on GBC) are aware of my reloading saga ... for those not familiar with it, the story to date is:
Shooting buddy and I split 5000 proji (125gn conical, 356dia) & 5000 (federal) primers.
He reloaded these in 9mm cases first and had tumbling issues. I've been using these proji & primers for years and never had a problem. However, when I eventually got around to reloading some I also had tumbling issues.
He increased his crimp, went up to 4.1grns of AP70N (which is what I'm using) and used only winchester brass and the tumbling stopped. I put some of his loads through my gun - great grouping and NO tumbling.
I used winchester brass, 4.1grns of AP70N and still had tumbling issues. On Monday night I reloaded 50 or so with more crimp, took them to the range on Tuesday and they still tumbled.
So back to the drawing board. OAL of his & mine are 5 1000's of an inch different. However, there is a marked difference in the width of the case at the base. So I got him to run 50 through his press doing the first stage only (primer out, resize) and then loaded them last night with different crimps.
I backed the crimp right off and then increased it by a quarter turn and loaded 5 at each point, taking it harder than it was originally.
Took them to the range today, and saw a marked difference in grouping but not in tumbling. I will now set the crimp to the best grouping and start looking at length as being the issue.
We tested the gun and the max length that I can load is 1216 OAL, his rounds are 1143, mine were 1138 (not sure what units these are - it's whatever his calipers measure!).
So I guess my next challenge is:
a) measure the rounds in mm on my calipers
b) load different test loads at 5mm increments from 1140 to 1210, using the best grouping crimp above and see if we can solve the tumbling issue.
If it's not this then I'm not really sure what to do next. (Oh, we pulled some rounds apart and double checked the powder - mine was exactly 4.1, his varied between 4.3 and 4.5, so maybe I could increase my powder just a touch).
It's been an interesting and educational challenge - but I really would like to find a solution :)