Just curious... you ever actually shot a .300 RUM? Not just 3-5 rds and then walk it off, but 20-25rds straight in 15-20 minutes, prone on the ground. Then wait an hour and do it again. Then again. If not, please tell me you're extremely recoil and blast tolerant? Remember, no muzzle brakes allowed in F-Class. gun)
I think you'd be the first that I've ever heard of even talk about shooting a RUM or similar round in F-Class. Not saying it hasn't crossed some people's minds, but not aware of one making it any further than that. Even in F/Open with a 22# weight limit, you *rarely*, as in like almost never, see anyone field anything much bigger than .300WSM, maybe .300WM. Some people are more recoil tolerant than others, but its a whole lot easier for most people to shoot and learn to read the wind with a lighter caliber. Surprisingly, it often more than makes up for any perceived ballistic 'disadvantage'...