Re: muzzle brakes
Just about any brake that will work for a .30 cal (.308) should work for the 300H&H. You'll probably have to have a gunsmith thread you barrel for it though. Depending on you barrel dimensions you may be able to get a brake that goes on with a set screw but wouldn't recomend that route. Especially if your looking for the best in accuracy.
I belive that most 30 cal stuff uses 5/8" X 24 TPI.
Good Luck
JMC