VaiB, 7 1/2 fills a niche like no other. It is a hot primer with a thick cup. CCI 450 is a LOT hotter. Many times I have found that the 71/2 groups smaller than the 450, many....
Winchester is a hot primer but has a thin cup.
I use a primer pocket uniformer on the Lapua on every firing, problem solved. Grit gets in the corners and does not allow the primer to seat fully.
Yes, I'm trying to stick with the Rem primers, being that's what my test loads are based on. The problem is with both brand new brass, as well as fired brass. I guess spending a LOT of time per case drilling the uniformer into the pocket helps. I have to drill long and hard enough so that the backstop plate of the uniformer is scraping the Lapua name on the brass. Only then does the pocket seem to be deep enough. Thanks.