Me and my dad both had 300 win mags A bolts with the Boss. I ended up trading mine in for a 300 wsm X bolt. The Boss was able to tune any factory load we put threw it below 3/4'' it is a great Gun he still swares by his. I traded because I liked the trigger 100 times better on the x bolt, I thought the clip added a nice touch and the safty open bolt feature. The new recoil pads on the browings x bolt are a wonder. the 300 wsm has some recoil. you wont notice it the kick, its more in the muzzle jump. Nothing bad.
I do wish they would put the boss on x bolts or at least muzzles brakes period that you can remove. I have one on my Christensen arms 30-378 weatherby mag and that kicks less than my dads 300 win mag with the BOSS. Christensens muzzle brakes take away about 40-50% where browing does about 30%
I do like shooting with out the noise of a brake, that the only down side.