Help understanding pistol chambers

[9teeneleven]

I have some basic questions regarding pistol chambers as they relate to reloading.

My first question involves the chamber depth, headspace, and the extractor. First, is dynamic headspace (as opposed to the static headspace of the chamber depth) determined by C.O.L. or case length?

If the answer is that the headspace is determined by case length, first, how does the extractor come into play? Second, why does C.O.L. matter for anything other than cartridge pressure and feeding?

Something that I ran across in my reading that is throwing me off is this picture:

The four different images imply that you can adjust headspace with your load. Should the bullet ever be touching the lands in order to obtain the ideal headspace?

This line of questions started when reading my loading manual and seeing that only max C.O.L. is listed not minimum (I am just getting started reloading).

[9teeneleven]

Probably need to add that I am dealing with .45ACP specifically.

[Guest Mugster]

Hmmm. Different cartridges headspace differently.

.45 acp headspaces on case mouth. Or another way to look at it is case length. The rim of the case should be flush with the back end of the barrel. If you put too much crimp on a .45 acp case, it might not headspace correctly. If the case stretches and you don't trim it, it might not headspace correctly.

When you say *only* feeding and pressure, you're saying alot.

In terms of the bullet touching the lands, thats another discussion, imo. I'd advise staying off the lands until you've been at it awhile.

Edited August 8, 2009 by Mugster

[gregintenn]

Mugster is correct. The auto cartridges headspace on the mouth of the case. If your case is trimmed to the correct length, you shouldn't have any problem with headspacing. I have found that straightwalled pistol cartridges rarely ever need trimming. Rifle cases need trimming regularly, as the higher pressures and the working in the sizing die stretches them. Most rifle cartridges headspace on the shoulder, save for the magnums, which headspace on the belt.

[gregintenn]

...to answer your qusetions, 1)If the mouth of the shell doesn't touch the step in the chamber, the shell is held in place by the extractor. Not a good situation. 2)Case OAL does affect pressure and feeding. I'm not sure how it affects handgun cartridges, but I find a big difference in accuracy in rifle cartridges using the same loads with different OALs.

[glockster157]

If the rimless straight walled case is to short and is being held by the extractor, then when the firing pin strikes the primer, the case can move forward and not receive enough force to fire. I have heard of folks shooting 40SW's in 10MM's if the extractor would hold the case tightly enough.

If the case is roll crimped instead of taper crimped, then the case mouth can move past the chamber lip that the case is suppose to stop/headspace on. When the cartridge fires the case cannot expand at that point because the case has been jammed into the bullet, so it holds onto the bullet until enough pressure is created to push the bullet out of that case. Usually this can cause a severe over pressure situation. Admittedly, this is hard to do with a pistol case but it can be done fairly easily with bottle necked rifle cases that have not been trimmed and are heavily roll crimped.