I had the same problem with Hornady factory 285 grain match... mic'd the case rim and found that it's on average .002" smaller in diameter than Lapua cases are. Never an issue with Lapua brass.

Another thing to check is the scope base screw that goes in over top of the bolt lugs... a few folks have found that the screw is too long, reaching into the bolt lug recess on the receiver. The tell-tale sign is a scratch mark on the outside of the left bolt lug.

The first 338LM's that Savage built had very tight chambers, with the lands very close. Pressures ran high. Hornady's match load was supposed to go 2650 fps from what Hornady says... but I was getting over 2800 fps from it. Just a simple issue of too much pressure...

More recent 338LM's from Savage seem to have more "ample" chambers. My friend's 111FCP (fcp I think it is) shows an extra .010" to the lands from what my early 110BA has.

That all said, his rifle and mine both shoot like customs... no kidding, super, super you-wouldn't-believe-it accurate. The same load works in both, an OCW load I developed about a year ago... 300 grain Sierra Matchking, 89.3 grains of Retumbo, in Lapua brass. CCI 250 or Federal 215 primer... this load gives 2700 fps almost exactly in both of our rifles...