Shouldn't be a gap between bolt face and the base of the cartridge. The cartridge seats on its belt, so normally there's no problem.
It's possible--just guessing--that the particular brand has problems with the belt dimension.
You could stick a small piece of tape on the base of the cartridge and see if more force is needed to close the bolt. Keep adding tape until you learn something. Again, I'd suspect problems in the dimensions of the cartridge case.
All guesses, though, mostly based on the comment that CoreLokt works okay.
FWIW, for many years the 139-grain bullet was the common loading in 7mm Mag.