I see nothing odd about it.
The 338 RUM is a great cartridge.
That long barrel plus brake is gonna cause you a bit of grief until you get used to that length.
Mine is a sporter weight carry rifle good to 1200 yds.
I stuff 101.5 gr of 50 BMG behind the 300 Berger. It shoots like and is as comfortable as a bench gun. The brake is only a Holland QD.
My heavy weights with the longer barrels are mostly for ambushing. Which is by far the most fun.
Good luck.
I'd also recommend Fed 215 primers not the GMs if you're going the Federal route.
It's been reported by those who should know and verified by me, at least with the lots I have that the 215 provides a bit more velocity than the match primer.