Quote Originally Posted by Scott View Post
I don't know what the term head space means. Can someone explain more?
Hi

When you put a round in the chamber you want it to only go in just so far. Some part of the bullet case has to hit the chamber somewhere to stop it moving forward. The distance from that point back to the primer end of the cartridge determines how far the firing pin is going to have to go before it hits the primer. On some cartridges the point that hits is way far back on the cartridge (the rim), on others it’s way forward (the case mouth).

You want the cartridge to fit in the chamber "loose enough" that the bolt closes. You also want the cartridge to fit in the chamber "tight enough" that the brass does not stretch to much when the cartridge goes boom.

On a cartridge like the 357 you force the open end of the brass down into a crimp grove (the cannelure) in the bullet (a full crimp). The cartridge headspaces on the rim so this works fine. If you look at a .357 you can see the brass "bending" into the bullet on a loaded round.

If you put a full crimp on a 45acp the same way you do on a 357 you are going to have trouble. The "mouth" of the round should be taken down below 0.471, but probably not below 0.4685 for most pistols. If you look at the 45 acp cartridge the walls of the brass are straight. If you do not get enough bullet tension with the mouth at 0.468 then the brass probably needs to be tossed or your bullets are under sized.

Bob