Its 25in. Well, the rifle is Blaser R93 so no bolt lift but ive heard you can get the same effect with pressure as far as not being able to cycle the action. I had no issues with that. Mule Deer says flattened primes in of themselves mean nothing. Old wives tale I suppose.
Flattened primers do not mean much, but when the primers fall out after four loadings, it does mean the load is too hot for the brass.
I often load one piece of brass multiple times to test for primer pockets becoming loose.
Primer choice? I have never found any thing better than CCI 250s in 30-06 or larger capacity using 4350 or slower powders. I would start with H4831 in your WSM, and perhaps experiment with Accurate Magpro or Ramshot Magnum as they are very dense and you can get high charge weights without compression.
The slowest powders in the IMR Enduron line look promising, but I have no experience with them at this time.
