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AR-15 extraction mechanism (Read 3194 times)

Thunder Chief Funditor Offline Don't Panic! Posts: 838	AR-15 extraction mechanism Dec 26^th, 2010 at 3:27am If anybody here uses an AR type weapon, could you possibly explain in excrutiating detail how the bolt system works, specifically how the mechanism grabs hold of the round and pulls it out, both when firing and when manually racked? Pictures would be helpful too, the closer the better! Thanks alot!
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Bikewer

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Re: AR-15 extraction mechanism
Reply #1 - Dec 26^th, 2010 at 10:26am

It's actually reasonably easy to explain. The extraction is much the same as any contemporary rifle, regardless of action. The fresh round, when stripped from the magazine, has it's rim slide under the spring-loaded extractor hook.
When the action cycles, the extractor drags the case from the chamber as the bolt moves to the rear. At the appropriate point, the opposite side of the case-head strikes the ejector, and is booted out of the ejector opening.

The bolt itself is a gas-operated turn-bolt system, incorporating a two-piece bolt (the bolt head itself, with it's locking lugs, and a carrier, which has the camming surface. When the weapon fires, gas is tapped off through a small hole in the barrel and travels back to the bolt through a tube.
The pressure forces the bolt carrier to the rear, which makes the cam surface turn the bolt head far enough to unlock from the breech.
Traveling to the rear, the bolt assembly performs the ejection chore described above, and also re-cocks the "hammer".
The recoil spring then drives it forward, stripping another round from the magazine to repeat the process..

A decent animation of the process:

http://www.youtube.com/watch?v=FZipq6D6D9k

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Re: AR-15 extraction mechanism
Reply #2 - Dec 26^th, 2010 at 10:46am

This probably should go under other topics, I don't think an AR 15 is all that primitive. Anyways, do you have an AR bolt you can look at or a picture? Basically, it pivots in the middle, on the end away from the face of the bolt, there is a small coil spring with a small rubber buffer in it. This pushes the end away from the bolt body. The end of the extractor that sticks out over the bolt face is rounded. When the shoulder of the cartridge seats in the chamber, the recoil spring drives the bolt carrier group forward. The bolt cam pin causes the bolt to rotate and lock behind the locking lugs in the chamber. This also causes the extractor to ride over the base of the cartridge and snap down in the extractor rim of the cartridge. This also compresses the ejector, that pin sticking up on the other side of the face of the bolt. When the rifle is fired, gas from the burning powder comes back the gas tube, into the bolt carrier and pushed against the gas rings inside the bolt carrier. The bolt carrier will start to move to the rear, compressing the recoil spring. As the bolt carrier moves, the cam pin causes the bolt to rotate, unlocking the chamber. The extractor pulls the cartridge out as the bolt carrier continues to the rear and the ejector starts pushing the cartridge away from the face of the bolt. The cartridge can only tilt so much because it is touching the side of the chamber and then the lug area. The ejector will force the cartridge case away from the face of the bolt as soon as the case is in ftont of the ejection port. Clear as mud? Any questions? Bill

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Thunder Chief Funditor Offline Don't Panic! Posts: 838	Re: AR-15 extraction mechanism Reply #3 - Dec 26^th, 2010 at 1:17pm Thanks guys, that's exactly what I was looking for.
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Masiakasaurus Forum Moderation Offline mah-SEE-a-kah-SOR-us Posts: 6069 Alabama, USA Gender:	Re: AR-15 extraction mechanism Reply #4 - Dec 27^th, 2010 at 8:49pm Bill Skinner wrote on Dec 26^th, 2010 at 10:46am: This probably should go under other topics, I don't think an AR 15 is all that primitive. Bill I agree with you. I find the engineering behind firearms really interesting, so thanks for the explanations guys.
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peacefuljeffrey Interfector Viris Spurii Offline Peace through superior slinging power! Posts: 2701 West Palm Beach Gender:	Re: AR-15 extraction mechanism Reply #5 - Dec 28^th, 2010 at 3:02am This video is a little better at explaining the steps, although I'm still not clear on what causes the bolt's rotating force as it goes either into battery or out of battery.
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