Is this safe? More specific- In a Glock 20/29? I have heard several times of someone who regularly does this, but how can it be safe? There would be no headspacing of the cartridge, and the only thing supporting the cartridge would be the extractor.

Ken,
I bet your reloading manual says NOT to do that...

My 2 cz 10's shoot 40's perfectly well.. feeds, fires, loads, fairly accurate

jeffe

There are quite a few folks on GlockTalk that state they routinely run .40 S&W though the stock 10mm barrel. Personally I have not and will not try it in my G20. For less than two bills one can purchase a KKM brand G20 barrel in .40. They are drop in fit ( At least my 6" hunting barrel was drop in fit)

Despite how good your medical insurance is your part of the bill will greatly exceed $200 should the gun not like the headspacing of the short cartridge in a long chamber. Just my take on it, your milage may vary.

I'm sure it can be done, but I think the extractor has to hold the case as it can't properly headspace? Seems kind-a stupid to me?

A lot of people do it with 380 and 9MM too. Just why I am not sure but if the round isn't caught by the extractor on the way in it simply fails to fire some of the time. The cases are roughly cylindrical so if it does fire it just scoots back to the breech face. With the pressures involved its no big deal like a bottlenecked rifle round would be.

I would expect it to work fine, as long as everything operated as it SHOULD. We all know STUFF HAPPENS!

I just can't see any good reason to do it. If you want light loads, load 10mm lite. If you want ammo availability, get a .40 bbl. With my Glock, I can swap bbl's in less than a minute!

Personally, I have no experience with it, but it seems that a bullet could try and hang on the lip which would ordinarily headspace the 10mm case. A 100 case is about .142" longer, compared to the earlier mentioned .380 vs. 9mm at .074", leaving more space for a case to slip in or a bullet to turn/lodge.

Finally, the best reason is that if the extractor does fail to hold the case and you practice a rapid fire jam clear (tap/rack/bang), can you imagine what happens? A live round fired into the back of another live round!?!?

The first 10000 shots you shoot might work fine, but 10001.....Not worth it, IMHO!