how does unsupported chamber lead to kaboom?
- Thread starter MJRW
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Basically a part of the case head has no metal of the chamber supporting it. This will be at the very end of the feed ramp. When the cartridge is fired the expanding gases forces against the case walls building pressure to force the bullet out of the crimp. The case swells to fit the chamber and when the case can't swell anymore the pressure then forces the bullet past the crimp and out the case. Where the case is unsupported the case can continue to swell till the metal fails and the gases blow out. This escaping gas has the force to possibly destroy a pistol.
stans
Member
But even with unsupported chambers, ka-booms are rare, if proper precautions are taken. 40 S&W seems to be the worst offender these days. The 40 operates at very high pressures and the case heads, at least in Federal brass, tend to be a little on the weak side. Now if you fire this factory 40 through an unsupported barrel, you probably won't have a ka-boom. If you reload, you begin to set yourself up for a ka-boom. As brass is expanded and resized, it work hardens. The area that is unsupported thins and also hardens. This creates a serious weak spot that is likely to rupture.
Another problem usually associated with polygonal rifling is the lead build up if lead bullets are used. This is not a problem unless the shooter allows the lead buildup to become excessive. This has the effect of placing a restriction in the bore and operating pressures skyrocket, leading to a ka-boom.
I think the most common causes of ka-booms are reloaded rounds with too much powder or a round without a powder charge followed by a live round.
Another problem usually associated with polygonal rifling is the lead build up if lead bullets are used. This is not a problem unless the shooter allows the lead buildup to become excessive. This has the effect of placing a restriction in the bore and operating pressures skyrocket, leading to a ka-boom.
I think the most common causes of ka-booms are reloaded rounds with too much powder or a round without a powder charge followed by a live round.
Clark
Member
Gun writer Dean Spier coined the term "kaboom".
Here is his web page:
http://www.thegunzone.com/glock/glock-kb.html
Notice the quote he has from me on the right
If you read Dean's page, you will see that the 40sw are bad and the 9mm have no trouble. My Glock22 40S&W
My Glock 22 40S&W has .235" fee ramp intrusion into the chamber.
A 40sw case has a web that is .180" thick.
That means there is .055" of thin unsupported brass case wall.
My Glock 19 9mm has .190" of feed ramp intrusion into the chamber. 9mm brass has a .160" thick web.
That means there is .030" of thin unsupported brass case wall.
9mm and 40 S&W are both 35,000 psi max pressure.
If a guy puts 30% extra powder in the case by mistake, which cartridge case do you think is going to blow a hole?
Those guys that blow their guns in half and not doing it with something as benign as 30% extra powder.
Here is his web page:
http://www.thegunzone.com/glock/glock-kb.html
Notice the quote he has from me on the right
If you read Dean's page, you will see that the 40sw are bad and the 9mm have no trouble. My Glock22 40S&W
My Glock 22 40S&W has .235" fee ramp intrusion into the chamber.
A 40sw case has a web that is .180" thick.
That means there is .055" of thin unsupported brass case wall.
My Glock 19 9mm has .190" of feed ramp intrusion into the chamber. 9mm brass has a .160" thick web.
That means there is .030" of thin unsupported brass case wall.
9mm and 40 S&W are both 35,000 psi max pressure.
If a guy puts 30% extra powder in the case by mistake, which cartridge case do you think is going to blow a hole?
Those guys that blow their guns in half and not doing it with something as benign as 30% extra powder.
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