I reload 45acp and have heard that the case headspaces at the case mouth. What exactly does this mean? What is headspace and why is it important? HOw do other cartridges headspace?

Headspace is simply the distance from bolt face to a point where the cartridge case makes contact with the chamber. The purpose is to hold the case back against the breech to prevent the case from moveing foreward, stretching and spliting when fired.
The 45acp and other straight walled cases do headspace on the mouth. The forward edge of the chamber should catch the edge of the case mouth and prevent it from moveing foreward. Timmed cases headspace on the rim, and bottle neck non-belted cases headspace on a point on the shoulder. Belted cases headspace on the belt. The belted cases can and often are sized when reloading by knowlagable loaders to headspace on the shoulder like unbelted. This is done by not touching the shoulder with your die when resizeing leaving it in the foreward position it was blown to when fired.

Head space is the distance from the case base to the breech face PERIOD.
Headspace is controlled by several methods eg. the shoulder, the rim, or the case mouth.
The dimensions that some people call "headspace" control these contact points.
Good luck!

hawkins,
Not to start an argument Sir, but I must dissagree with you. By SAAMI definition headspace is the distance from the breech face to a datum dimention within the chamber. The cartridge design determains how it controlled.

In simple application it is the distance from the breech face to the cartridge head, but not by definition nor is it measured this way in practice.

Ol' Joe has it correct.

Rusty; Ask yourself; If headspace isn't the space at the head of the case, why is it called that. People often confuse the datum measurement
with the clearence left between the datum measurement and the breech face.
As an example; Cleveland and New York are 500 miles apart, but their locations are measured from the Prime Meridian in England. When the width of the atlantic was corrected by satellit measurement New youk didn't move a bit.
Good luck!

quote:

Originally posted by hawkins:
...If headspace isn't the space at the head of the case, why is it called that. ...

That is simple enough to answer, because the term is used by some folks to mean one thing and by others correctly.

Some would be more accurate to say "Amount of Headspace or Excess Headspace" when talking about the distance between the Boltface and Casehead.

To help you out with the who is right and who is wrong, Ol`Joe and Rusty are both correct. And in some discussions, Rusty is partially correct.

Kind of like anyone recommending B&W over S&S for a hunting rifle. B&W will no doubt work, but S&S is simply a w-a-y more correct answer.

(p.s. I saw your slam on S&S in mho's Weatherby thread on the GunSmith Board. )

Hot Core; that wasn't a slam, I was defending Weatherby's. To each his own.
Good Luck!

quote:

Originally posted by hawkins:
Rusty; Ask yourself; If headspace isn't the space at the head of the case, why is it called that.

Hawkins

I'll take a stab at your question. Most of the earliest cartridges were rimmed and the rim was often called the "head". The distance between the breech block and the end of the barrel was the space for the head, or, the "headspace". The modern-day headspace for a rimmed cartridge is indeed the distance from the breech face to the front of the rim not the distance from the breech face to the rear of the rim. Over time with the introduction of rimless, belted, rebated, semi-rimmed, etc, etc the term headspace was less accurate than it was originally but it is and always has been the distance from the breech face to a point on the case that stops its forward movement into the chamber. This subject has been kicked around so many times on the different shooting forums and the arguments are always the same. I say, call it whatever you want and I'll call it what I want. In the end we know what the other guy (right or wrong) means when he says the word "headspace".

Ray

quote:

Originally posted by hawkins:
...I was defending Weatherby's...

Hey Hawkins, Nothing at all wrong with Weatherbys. In fact, I have a S&S Wby U-Lt.

Good hunting and clean 1-shot kills to you.

what's this?????...someone slammed weatherby and I didn't cheer him on?????....I must be slipping here.

quote:

Originally posted by vapodog:
what's this?????...someone slammed weatherby and I didn't cheer him on?????....I must be slipping here.

Hey Vapodog, I've always thought the rifle you have laying on the cow you are hiding behind with the funny horns was one of these:
https://forums.accuratereloading.com/eve/forums/a/tpc/f/9411043/m/638100593

Might as well get this New Year kicked off correctly. How's your "Headspace" doing after all the celebrating?

Now, boys..., no ad hominem insults allowed.

Joe45: Headspace is very important to control in rifle cartridges, but for the 45 ACP, well I don't worry about it.

I shoot my 45ACP ammo in either M1917 revolvers or in M1911 pistols. The M1911 has an extractor that holds the cartridge against the breech face, (within reason, there is a little movement). With the 45 ACP being basically straight and held against the breech face, there is a very small chance of longitudinal stretching during combustion. This is the big worry in a rifle, the possibility that the case is stretched lengthwise more than the brass allowable.

My only real concern with 45 brass is whether it is too long. If it is too long it will cause jams in the Autopistol.

I shoot my 45 ACP brass in different pistols, full length size, and shoot the stuff until it gets lost on the range. Don’t worry about pistol headspace.

Do worry about rifle cartridge headspace. When you start loading rifle cases, use headspace gages, like the Wilson gage, to determine how much you are setting the shoulder back. And trim the case each time (or measure it). This should keep you out of 95% of the trouble a new shooter will get in with sizing rifle ammo.