Just wanted to add my .02
I'm not sure what the weight of a .300 RUM in a sendero but i would say atleast 9 pounds. Now I have a DE break on it and a custom barrel but it's still the sendero contour without the flutes . The break made it a totally different gun to shoot. recoil wise.
I have shot 7mm to 300 winmags since I was 15 years old and they had the little skinny barrels . So I aint recoil scared but I found out that the heavier the better .
A 9 pound .300 RUM without a break loaded close to max on the powder scale (if you shoot from a bench with light clothing will STOMP YOUR GUTS OUT !!!
If I where a betting man I would put money on it that know matter how well you shoot you will shoot better with a .300 RUM Or .338 EDGE/ Lapua Braked than not braked . Just look on this site for example what is all the guys shooting with at 1000 and beyond they are using big calibers packed full of powder and a nice tank style brake ....