Always nice to get perspective from somebody that shoots no sanctioned BR, though the ever popular 50 BMG is probably coming on strong.
To the OP, Flat bottom, usually 1/2” is very common, get a proper rear bag with ears spaced to fit that stock.
Opinions may vary but with proper ear spacing the stock rides on the bottom between the ears. A 30 is going to want to rotate on recoil but a good rear bag setup helps.IMHO can’t shoot a 30 free recoil.
Given the questions I assume your a rookie, thus use the stop, it allows your gun position to be absolutely repeatable until you get accomplished at gun handling throughout a match. Get the absolute best front rest you can afford as well as a quality rear bag and do not fill them rock hard, as they then get “bouncy”.
Lastly, watch some of the videos out there and/or better shooters at a match to learn to stay on the gun with little moving around and wasted motion until you can comfortably, with no rushing get five shots in a group in 15/20 seconds.