ill have to measure to make sure im not missleading you, but a bullet fits tights into the case so the case will likely have an inner diameter just a bit smaller than the bullets outer diameter.
just checked, my .308 bullet measures exactly that, my die crimps the inner diameter of the case to about .305-.306 right in that range, i dont have any clean brass but thats some that have been recently fired.
not sure what he meant about firing the primer. although i think what hes refering to is to get rid of the primer so that you can crimp the case properly and hes saying to fire off the primer and then crimp them.
you prime, then add powder then the bullet goes in.
i know my de priming die crimps as it pops the primer out