7.62x39 is a bottle neck cartridge. Bottle neck cartridges "head space" on the shoulder of the cartridge case. [Read in your reloading manual about head spacing for bottle neck cartridges.] Since these cases came from ammo that was not fired in your gun, you'll have to reset the distance from the shoulder to the base of the cartridge by doing what's known as "
bumping the shoulder". In other words, this brass is too long for your chamber.
Basically, you're going to FL resize this brass and relocate the shoulder to a ever-so-slightly lower position by screwing the sizing die down a tiny bit further. Then you're going to try it in your gun, and bump it down again until the bolt takes slight amount of pressure to close. Not hard, but not easy either. You'll want to lock the die down when you find that position, because that's the length of your chamber and
every piece of brass you FL resize from now on is going to need that exact same distance.
If you have the type press that requires you unscrew the sizing die, then you're going to need some
locking type die lock rings (e.g. Hornady) so that the die returns to that
exact position at every future setup.
Once the brass has been fired in your bolt rifle, all you'll need is a Neck Sizing Die and things will go much faster.
Hope this helps.
