In the old days we put some dacron filler wadding in to hold powder back next to the primer, there were worries of "detonation". I (and everyone else) stopped doing that long ago as it turned out to be unnecessary, just an extra step, time and expense. I use 47 gr of RL 7 under my 300gr HP's, but have used as little as 35gr, and I use 32 gr of 4198 under 385 gr cast, so space is not really a problem unless you are having accuracy problems due to inconsistent ignition.