I know the burn rate of some powders are slow and some are fast. What chance does gas get to flow around a yet to be propelled correctly crimped bullet? Or does it all equal out uniformly?
Thanks

Yes it does.

F. Guffey

Gas will flow by. Not sure crimping will change anything.

You can't stop it and bullets aren't always a perfect seal even after they engage rifling. . Look at some video of bullets exiting barrels and you will see gas before the bullet. Hopefully, it will be minimal and uniform. Lead bullets that upset are best and you have to have a perfect seal here or the gas will cut them and lead and other bad things will happen.