First-off --- hearing is a very important sense, no reason to try and damage it on purpose. If possible, you should always try to use hearing protection while pulling the trigger or spoting for someone. LRH allows the ear gear to be put on and that is the #1 reason my 338 has a break.
I have shot a 300RUM w/out a brake, 26 in barrel and it was not fun, but only weighed about 7 lbs, with a break ---same rifle, felt like a .243. The other 300RUM was abou 11.5lbs, no break, 30inch barrel, and was ok --- just had a gentle pushback ----- I think it had to do with a good stock,pad system and the longer barrel burning the powder more thoroughly.
Several years ago I developed a terrible flinch problem by shooting 3 1/2 inch 12 gauge turkey loads in a mossberg pump --- likely due to bad stock design and, light gun and heavy recoil, ---- I corrected it by shooting a lot of rounds with less recoil, but speaking from experience, don't put yourself in that situation if you can avoid it.
I would suspect that a 300RUM at 11lbs with a long barrel and good stock design would be fine w/out a brake.