Depending on powder used it could've gone either way on speed. With it being sealed on 1 end it can and have to exit the muzzle. With that being stated the fastest burn rate powder for that cartridge combo it would have a lot of bolt tension (back pressure). Something with lots of gas volume at near max pressure will continue to speed up and keep the momentum going. I look at it like the difference between natural gas and propane. NG is a volume user with very low pressure (5 - 12 oz) and propane is the opposite.