I know the military manual states "your rifle ... will explode." Why?

My guess is that the bolt won't lock without it and the pressure will blow a ton of gas back, throwing the bolt carrier toward the buffer. But why would it explode? Does the bolt carrier move fast enough to break things up? I'd imagine that the gas would escape out the ejection port so I am slightly confused.


P.S. I am not interested in test firing to find out. I put the cam pin back in and gave it a 1/4 turn as stated

Well the cam pin is what rotates the bolt's locking lugs into the barrel extension. Without the cam pins the bolt would not lock, the cartridge would fire and with no locked breech it would most likely explode.

In normal operation with a cam pin. The bolt is locking the chamber sealed. The bolt carrier does not move at all untill the bullet passes the gas hole in the barrel. At that time the explosion of the cartridge is over and chamber pressure is reduced ready for extracton. So now the gas goes to the bolt carrier and moves it back unlocking and pulling the bolt from the barrel extension and the empty along with it.

I assume it would act the same as an out of battery fireing with the brass bursting due to not being supported by the chamber.

You know, that makes sense... without the chamber for support, the brass would explode. But would the rifle itself explode?


Dave: yeah, I've familiarized myself with gas operation. I knew the bolt locked and guessed that the cam had something to do with the actual locking.


I know this all seems old-hat to posters here, but I have yet to find any source online that describes the complete firing cycle so I am guessing and working my way through it, attempting to determine exactly how the whole business works.

Unless you are quite familiar with the equipment you use, you are nothing more than an end-user, and no one wants to be an end-user [;)]

Notice when putting your rifle back together sometime how without the cam pin you can rotate the bolt like a wheel.  If you fire like that the bolt wont rotate properly locking into place.  Instead of using all the energy from ingnition to force the bullet down the bbl. it will force the explosion backward and everything behind that explosion will essentially become shrapnel to a certain degree.

Not an AR but...

I had a case failure from a breech that hadn't closed all the way. It was a .357 Sig. 40,000 PSI chamber pressure.

Got my attention [BD]

"your rifle ... will explode." Why?

The high pressure gas can only flow through the ejection port at a certain rate. Although it's a gas, it still has mass and is subject to inertial forces. The pressure inside the receiver rises sharply for an instant while the gases exhaust out through the port. The ejection port is relatively small compared to the inside surface area of the receiver and magazine. Consequently they bulge and get blown out.
Another example of this is a rocket engine. Although the gases are able to escape through the exhaust, there is still enough pressure inside the chamber (against the front) to push the engine forward.

Dont forget with an AR I think we are talking what 50,000 or maybe its 52 PSI,I wouldnt want that blowing in my face,

Why will it explode?

Because if you tell some dummy who really has no idea how a weapon works that if he doesn't install the cam pin, his rifle will EXPLODE in his hands, he will most likely remember to do it!!!

It is also very important to know that the rifle is 8.79 lbs with a 30 round mag and that it is 39 5/8" long [BD]

Sgt. Johnson told us the really nasty one was to forget to install the firing pin retaining pin, though he never explained why...

Well with no retaining pin I'd imagine that the first time you hold the rifle with the barrel pointing up the pin would fall out and then it wouldn't fire.

Or worse, when you fire and the gas unlocks the bolt, the bolt will go flying back with the pin in tow. When the bolt starts impacting the buffer, I'd imagine the pin will just keep on sailing (think passenger without a seatbelt) until it hits the buffer too. So now it isn't inside the bolt anymore. Then the buffer spring recovers and starts pushing the bolt forward. Odds are good the firing pin won't be pushed back in its proper place now and will just rattle around inside the bolt carrier.


But this is my ameteur guess! Correct me please, if I have made a mistake.

Go to [url=www.armalite.com]Armalite's website[/url] and, in the left toolbar, click on "movies".  The second one that's listed is an old training video for the Army, which includes a pretty good description of the firing cycle.  

D_H is right on the money here. If the lugs on the bolt line up with those of the extension, the carrier will close (exposing the firing pin to the hammer) but the bolt will not rotate into the locked position. Hence, a very serious problem. This is worse than an OOB kB bc the case IS fully supported but the action will open as soon as the pressure is high enough to force the bolt (not the carrier as is usual) to the rear. The pressure only increases from there as the gas expands. It is easier for the gasses to vent through the base of the cartridge (large orifice) than through the bore (small orifice).

As opposed to an OOB kB that usually causes the case to fail and the propellant gasses vent through the failure ala a case head separation.



If you leave out the retaining pin the firing pin will come out. The firing pin keeps the cam pin from rotating. If the cam pin rotates it will wedge in the upper receiver and you'll have to take the gas tube out and tap the cam pin back into alignment using a long probe. Same same if you leave the firing pin out.

[speeling]

And this, my friends, is probably the REAL answer.

Think of it this way.  The 5.56 mm round develops about 4,500 to 5,000 lbs of bolt thrust when the cartridge fires.  Without the benefit of the locking lugs, the rifle will be operating in a straight blow-back mode, fine for small pistol calibers, but not good for high-pressure rifle cartridges.  Now, you will have a situation where you have a bolt and carrier weighing approximately 1 lb, flying rearwards with 5,000 lbs of force.  The rifle is unlikely to stay together in that situation.  

KAFRICKIN BOOOM!

whos ressurecting old threads? huh, who is it?

Man that seemed like so long ago but it was only a month! Seems like a silly question now.