I've been lurking for awhile and need advice/help. New (factory) model 12 .260, virgin Lapua brass 39 gr. of H4350 cci br2 and a 139 Lapua, .020 off and it almost blows the case head off. Headspace is good with a ptg and Forster go gauge. Same components with 34.5 Varget and it shoots about 1/2 moa, but really slow and leaves a ring near the case head.
Kinda reluctant to buy another batch of Lapua. I did buy some Federal fusion 140g at it shot a 6" at 100. Yeah, 6" at 100. I tried that brass with the 4350 load and neck sizing between the brass stayed together.
So, is the Lapua brass generally an issue with saami reamed chambers? I had this rig over 2 years and I'm beginning to become frustrated. Any help is greatly appreciated.

edit: my goal here is to find a combination of components that work, not to place blame on a component company or the rifle maker.