Descreet38
02-01-2009, 01:15 PM
While this isn't new "NEWS" it is important. As stated in the article this really becomes improtant if you are shooting a Glock or another firearm that has a long feed ramp which equals a very unsupported shoulder at the bottom of the cartridge.
I have seen several 40's go KB from this but I have never experienced a problem. I shoot a S&W 4006 which of course was developed for this round to begin with.
Case failure reports
http://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Beretta96_FeedRamo.JPG/120px-Beretta96_FeedRamo.JPG (http://en.wikipedia.org/wiki/File:Beretta96_FeedRamo.JPG)
Beretta 96 Feed Ramp
The .40 S&W has been noted in a number of cartridge case failures, particularly in Glock pistols due to the relatively large area of unsupported case head in those barrels, given its high working pressure.
The feed ramp on the Glock .40 S&W pistols are larger than normal, which leaves the rear bottom of the case unsupported, and it is in this unsupported area that the cases fail. Most, but not all, of the failures have occurred with reloaded or remanufactured ammunition. Cartridges loaded at or above the SAAMI (http://en.wikipedia.org/wiki/SAAMI) pressure, or slightly oversized cases which fire slightly out of battery (http://en.wikipedia.org/wiki/Out-of-battery) are often considered to be the cause of these failures. These failures are referred to by many as "kaBooms" or "kB!" for short. While these case failures do not often injure the person holding the pistol, the venting of high pressure gas tends to eject the magazine out of the magazine well (http://en.wikipedia.org/w/index.php?title=Magazine_well&action=edit&redlink=1) in a spectacular fashion, and usually destroys the pistol. In some cases, the barrel will also fail, blowing the top of the chamber off.
http://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Beretta96_ExtractorNotch.JPG/120px-Beretta96_ExtractorNotch.JPG (http://en.wikipedia.org/wiki/File:Beretta96_ExtractorNotch.JPG)
Beretta 96 Extractor Notch
While the .40 S&W is far from the only cartridge to suffer from case failures, it is more susceptible for a number of reasons. The .40 S&W works at fairly high pressures (33,000 psi/230 MPa typical, but 35,000 psi/240 MPa SAAMI max) for a large caliber handgun cartridge, significantly more than, say, the .45 ACP.
Since the .40 S&W is a wide cartridge for its length, and is often adapted to frames designed for the equally long but narrower 9x19mm cartridge, the length of the feed ramp must be longer to provide the same angle, which causes the feed ramp to extend into the chamber. This in turn leaves more of the case head unsupported. While this is not necessarily unsafe, it does reduce the margin of safety. When exacerbated by out of battery firing (leaving even more case head exposed) and potentially weakened brass (due to reloading) these factors appear to lead to the higher incidents of chamber failure. The number of case failures in the .40 S&W is serious enough that Accurate Arms no longer recommends reloading of .40 S&W cartridges for firearms without complete case head support.
I have seen several 40's go KB from this but I have never experienced a problem. I shoot a S&W 4006 which of course was developed for this round to begin with.
Case failure reports
http://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Beretta96_FeedRamo.JPG/120px-Beretta96_FeedRamo.JPG (http://en.wikipedia.org/wiki/File:Beretta96_FeedRamo.JPG)
Beretta 96 Feed Ramp
The .40 S&W has been noted in a number of cartridge case failures, particularly in Glock pistols due to the relatively large area of unsupported case head in those barrels, given its high working pressure.
The feed ramp on the Glock .40 S&W pistols are larger than normal, which leaves the rear bottom of the case unsupported, and it is in this unsupported area that the cases fail. Most, but not all, of the failures have occurred with reloaded or remanufactured ammunition. Cartridges loaded at or above the SAAMI (http://en.wikipedia.org/wiki/SAAMI) pressure, or slightly oversized cases which fire slightly out of battery (http://en.wikipedia.org/wiki/Out-of-battery) are often considered to be the cause of these failures. These failures are referred to by many as "kaBooms" or "kB!" for short. While these case failures do not often injure the person holding the pistol, the venting of high pressure gas tends to eject the magazine out of the magazine well (http://en.wikipedia.org/w/index.php?title=Magazine_well&action=edit&redlink=1) in a spectacular fashion, and usually destroys the pistol. In some cases, the barrel will also fail, blowing the top of the chamber off.
http://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Beretta96_ExtractorNotch.JPG/120px-Beretta96_ExtractorNotch.JPG (http://en.wikipedia.org/wiki/File:Beretta96_ExtractorNotch.JPG)
Beretta 96 Extractor Notch
While the .40 S&W is far from the only cartridge to suffer from case failures, it is more susceptible for a number of reasons. The .40 S&W works at fairly high pressures (33,000 psi/230 MPa typical, but 35,000 psi/240 MPa SAAMI max) for a large caliber handgun cartridge, significantly more than, say, the .45 ACP.
Since the .40 S&W is a wide cartridge for its length, and is often adapted to frames designed for the equally long but narrower 9x19mm cartridge, the length of the feed ramp must be longer to provide the same angle, which causes the feed ramp to extend into the chamber. This in turn leaves more of the case head unsupported. While this is not necessarily unsafe, it does reduce the margin of safety. When exacerbated by out of battery firing (leaving even more case head exposed) and potentially weakened brass (due to reloading) these factors appear to lead to the higher incidents of chamber failure. The number of case failures in the .40 S&W is serious enough that Accurate Arms no longer recommends reloading of .40 S&W cartridges for firearms without complete case head support.