Sorry I missed the question, yes I foul with 10-12 rounds after cleaning, before shooting for accuracy. Currently I'm cleaning between 110-130 rounds.
You can work with the powder charge. I load several cartridges over the manual stated max load. I fully under stand the quest for velocity. I am very much the same way. I have Peterson brass in 280AI and found right out of the box they varied several thousand in length from case to case. i went through 30 to 40 pieces of brass and they inconsistence to say the lease. There been a lot of talk about when to trim cases. From what I have read that different case lenghts changes the release of the bullet. I can't prove that one way or the other, but I can see it causing problems.
Now I cut my necks for thickness from the get go. I start with making sure all my case are the same lenghts, then cut for thickness. I have a 6mm/280AI chambered rifle with a 30" heavy barrel, 7-1 twist rate. I had a reamer made for it. The reamer ended up cutting a little tighter in the neck area by .001. So I am having to cut my necks to .0012th. The tools I am using are automated. So I set up everything to be the same. So case length is very important to me. I don't want to cut into the start of the shoulder from the neck. That was one of the reason I went to a 280AI case was for more powder charge. I also having 25/280AI being built.
Being you are using an AI case, they suppost to not grow much. That probably why you are not seeing the cases growing much if any.
I put together a 34 page doc on general procedures and case prep. It's make up from other people and what they have stated over the years, and I reduced it to the form I have now. There is thing that I have found that work also and placed into the doc.
In thinking about your problem. Possible to set up with a neck sizing die and only size the neck partly, leaving about 1/4 of the neck unsized, so it chamber size for part of the neck. I stumble on to this a great many years ago with my 308NM rifle. The 308NM case is shorter to the shoulder than the 300WM case. The necks on the 300WM are shorter than the 308NM cases. So I tried a 300WM neck sizing die to resize my brass. It size the case about 2/3 the lenght of the neck. So I end up with a kind donut shape in the neck area. It did two things. It stop the case separation dead in it's tracks, and my accuratic improved just a bit. I would lose a case in 3 firing and after that I would lose case do to primer pocket would get to big to hold a primer any longer. That was after about 10 to 12 firing. No more case separations. My loads are about 5grs over the max shown in the manuals. That was using H4350 powder, and Fed 210 primers. I tried 215 primes but couldn't get the velocity out them and the accuratic decreased too. The H4350 is faster burning powder and help with the velocity.
I could got about 100fps with IMR powders, but the temp got me in only about 50 dr weather change. I blew a primer out of the case into the action. That load was also about 5gr over max. So I never use IMR powder in my rifle every again. There only 3 rifle I use other powder in. Is my 338WM 25/06 and 220 swift. I am have a 338 WM being built in a 28" barrel to see if I can acheive the same velocity as I get in my Ruger Mark 11 with a 24" barrel but using H 4350 or some other H powders. I'll never cross that bridge again with IMR powders.
The worst of it was I took down my reloading area. I planned on using my son exter area in the garage to relaod in. His wife figure she wanted it for an office. So I lost out. No biggy, but then I had to come with another spot, and building. I make it to be portable. We have trucks that can pick it up and move it to a different location if need be. I am finally just about to complete the reloading shack. I think I'll be back into the reload ammo again a few weeks.
. After 250 rounds of speed graphing for nodes, SD graphing and seating depth test and graphing and going on my 4th bullet and 3rd powder. If this were a tuning issue it would be over long ago.
