Extractor as Headpace Determiner

[williejc]

One fact that .45 Auto shooters have known forever is that the case often headspaces on the extractor. How? The extractor's grabbing the case can and does limit its forward movement in the chamber. Of course we all know that the .45 ACP round was designed to headspace on the case mouth. However, a shorter than standard round will headspace on the extractor. The truth is that we can not distinguish whether headspace is being arrived at by extractor or case mouth. These statements apply to all semi auto cases designed to headspace on their case mouths.

Everybody knows that if a .380 Auto round is placed in a 9mm L. chamber, it'll slide forward and can't be fired. But if you will load .380 ammo in your 9mm L's magazine, insert the mag, and rack the slide, then it will chamber, be held by the extractor, and fire. You can then, rack the slide, and fire again. I've done this numerous times over the years. The point here is not WHY do this. The point is that this explanation illustrates HOW extractors can set headspace in some pistol rounds. I did it to experiment but certainly am not saying that anyone else should.

But i started thinking. Let me experiment further. I have had a Glock 20 10mm for many months and began to wonder why I could not safely shoot 40 S&W ammo in the 10 mm barrel. So after having fired at least 1000 40 S&W hand loads through my Glock 10mm using the factory barrel, I can report that in my experience with my hand loads and in my pistol, I had zero failures with zero bulged cases. Accuracy was good with the one load that I used. And guess what? I was shooting lead bullets cast extremely hard from linotype. Over the years I've safely and with zero issues fired lead bullets(always hard) though Glock 9mm, .40 cal, and 45 ACP barrels--like since the late 1980s.

In no way am I suggesting that anyone else follow my example. You may blow your gun up. And I know that Glock would be horrified. So spare me on this point.

[26 Inf]

What was your rate of fire? I don't think that it would make any difference - just curious.

Also do you think the bullet shape and OAL of the round had anything to do with reliability? I guess the 10mm mag held it to hit the feedramp at the right angle enabling the case to slide under the extractor.

[williejc]

Rate of fire was up and down the scale. I knew it would feed ok because many other people have used Lone Wolf and other conversion barrels without issue. Also I'm not the first here to have tried firing the shorter round in a 10mm barrel. It worked uncannily great. Eventually I'll seat the bullet out further to permit more powder to mimic full 10mm loads, which I don't really need. This arrangement allows reliable feeding of 40 S&W ammo because there is very little difference between the length of the two cases. Too, the 20's larger magazine permits seating bullets to greater overall.

The purpose of posting the thread was explaining extractor/headspace information to younger members that may not have been aware. I included the rest of the story as an after thought. One other trick for establishing 45 Auto headspace is setting the bullet out just far enough that it contacts rifling. Guys elected this procedure to make every round have exactly the same position in the chamber. I'm talking about bulls eye shooters who are OCD to begin with. Did it work? My opinion is that it wasn't worth the trouble. Some of these folks were convinced that a pitted barrel shot better than a non pitted one because it would hold more bullet lube. They would then take a new barrel and treat the bore with salt water to corrode it. I'm convinced that this proved that a crappy bore could shoot well too. Then a brand new Colt surplus barrel was $5.00.

[Bubba FAL]

Interesting. I experienced some of this learning curve during my dalliance with .45 Super 20 plus years ago. Trimming cases down to fit the chamber of my Colt was eye-opening for sure.

[Clint]

Here is a good article on the topic.
http://www.thetruthaboutguns.com/201...-a-10mm-glock/

[T2C]

DO NOT TRY THIS.

When I ran our range a retired officer showed up for his annual firearm qualification. He was not shooting groups as tight as I remembered he was capable of doing. He finished the first three stages and started to have malfunctions at the 15yard line. He asked me to take a look at his Glock 22 to see if something was obviously wrong. While I was giving his weapon a cursory inspection I heard him utter a few profanities. He told me he had to retrieve something from his truck and disappeared.

The retired officer returned with a box of .40 S&W ammunition. He had completed the first few stages of his qualification firing 9mm ammunition through his Glock 22. The first 25 rounds of 9mm fired and functioned properly. Not only was the brass too short, the projectiles were 0.046" smaller than the bore size.

A good extractor will often allow you to fire ammunition that does not headspace properly. It is not recommended though.