The only Bertram brass I've used extensively is the 375 CheyTac brass I use in my 338. It's good strong brass, but the rims are inconsistent. The diameters and thickness on the rims is enough of an issue that I have to actually sort it. My BAT action with a sliding plate style extractor will take all of it but the Lawton's Sako style extractor struggles with probably 10% of the brass.
I'm on 5-6 firings on most of my cases and the primer pockets are still as tight as the day I got them, so it seems to hold up pretty well. I don't push it very hard though. That was the whole reason for going with a case this big. I'd rather throttle back a large case than red line a smaller case (338 Lapua improved) to get the same performance.