Unsupported chambers.

[PinnedAndRecessed]

I read about a guy's gun which blew apart. It was a USP 45. Someone said that frequently resized cases fired from guns with unsupported chambers are accidents waiting to happen. He mentioned specifically 40 S&W out of a Glock, USP or any gun with unsupported chamber.

What's he talking about and what kind of guns have unsupported chambers? My Sig 220? My Mk 4/Series 70 Colt? My soon-to-take-delivery Colt Combat Commander?

 

[Sheldon]

I think most designs are "unsupported" but have been that way with no problem for many years. The 1911 design is also unsupported unless you have a "Ramped barrel" in it. The unsupported area is where the barrel opening is flared at the bottom to allow the round to feed into it. That flared out section leaves the case unsupported at the bottom in an "unsupported" barrel. In a barrel that is fully supported the flare will not expose any portion of the web of the case. Weak brass or overloaded rounds may cause the case to blow out in that area. When the IPSC crowd started to really load up the 38 Super to make major power factor they ran into a lot in the beginning and they called it Super Face from all the debris that blew back into the face of the shooter when a case gave out. The higher pressure cartridges are more prone to this than say the lower pressure cartridges like the 45 ACP, but I would not worry too much about it as long as you don't reload super hot loads all the time with old brass...or use lead bullets in Glocks whose barrels lead up.

 

[Dave R]

The Kel-Tec P-3AT has an unsupported chamber.

When I was working up handloads for it, there were loads that approached the published maximums, that worked fine in my PPK clone, but left noticeably bulged cases in the P-3AT. Too close for comfort. I backed off the loads.

 

[Chipperman]

Any gun with a feed ramp has some loss of support. Some brands have less support than others. People trash Glocks because they have less chamber support than other guns. HK's and Sig's have more. Does this matter? It depends on who you talk to.

Bottom lines are:
1. Any gun can KB!
2. .40 S&W tend to KB more often as it is a high pressure round.
3. Most KB's are the result of impoperly reloaded ammo, and are not the gun's fault.

 

[Technosavant]

I don't think anybody has given a definition of an "unsupported" chamber.

That would be when the chamber does NOT fully enclose the case of the cartridge (with the exception of the rim). The idea is that the pressure-bearing part of the case is reinforced by the chamber. If a gun has an unsupported chamber, and pressures are high enough, the case may bulge, crack, or in extreme cases, you get a Kaboom! (rapid firearm disassembly, very dangerous to the shooter).

This is really only an issue with high pressure rounds (+P anything, .40S&W). .45ACP is relatively low pressure, so the standard unsupported chamber (at the rear due to the frame ramp design) is not a big deal. Like was said, a ramped 1911 barrel is fully supported.

 

[Rockstar]

Technosavant: How about giving a little evidence of ANY firearm's having a "polygonal chamber?" Maybe you should reconsider your username?

 

[unclestu]

Polygonal *chamber*? I can only say that my ~1993-94 vintage Glock 22 has a polygonal *bore*. It has a plain ole round chamber.

 

[Technosavant]

Oops.

I read that from a Glock supporter.

You mean you can't believe everything you read on the internet?