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Posted: 2/18/2009 9:19:18 PM EDT
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I have a full-auto Bushmaster with a 10.5" barrel that is not running correctly on full-auto. Semi auto is flawless, but on full auto I get stoppages. Sometimes one round fires and the gun dies bolt-closed and sometimes two or three fire before it dies bolt-closed, the number is completely random. I have even gotten off strings of 10 to 20 rounds but eventually the stoppage occurs, I cannot get through a 30-rnd mag. It is not stance or grip realted, I am 100% sure. My gas key is staked and tight. NOW here's the key piece of info: When the stoppage occurs, I manually eject a round that did not fire but has a light primer strike on it every time.
Any armorer suggestions will be greatly appreciated, I think I may need to slow down my rate of cycle but I already have an "H" buffer in it. Thanks. |
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First off, you need to figure out the release gap of the hammer from the sear.
To do this, use a gauge or the back end of a drill bit, and while tapping the trigger back and the selector set on auto, pull the charging handle back and stick a gauge/bit in between the front of the carrier, and the back of the barrel extension through the front of the ejection port. With a gauge/bit #43 (.081), the hammer should be released from the auto sear. With the gauge/bit # 46 (.089), the hammer should not be released from the sear as you walk the bolt forward. The idea auto sear release gap between the face of carrier and the back of the barrel extension is .083, but get the timing to release withing these too sizes and you can call it good. Should note, when the timing is too advanced, then the hammer is released before the bolt has started to cam'd closed in the carrier, and the back of the carrier is blocking the FP from fully protruding and igniting the primer (bolt not locked up yet, so that is a good thing to happen). __________________________________________ Now if the auto sear release gap is in the correct range, then you are running into problems with bolt bounce, being that the carrier is bouncing back away from the barrel extension as the same time as the hammer is trying to strike the FP (after the bolt has locked up), and the back of the carrier is blocking full protrusion of the FP. Here, going to a heaver buffer, such as a H-3 should solve the problem if you don't run into short stroking problems since it will prevent bolt bounce (control the carrier so it does not bounce back after lock up); again as long as the release timing is within spec and the hammer is not trying to strike the FP before the B/C even has a chance to lock up in the first place. Note on the H buffers, The number behind the H stands for the amount of tungsten disco that the buffer has to add weight. There are three discs in a buffer, so if the number was 2, it would have two tungsten discs, and a standard steel disc. If you have a H-3 buffer, and a standard buffer, then you can make any of the H series buffers by just swapping discs between them. The H-3 buffer will have three tungsten discs, and the standard buffer will have three standard steel discs. |
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Thanks alot Dano, I checked it out and the auto sear release gap is in the correct range, so i'm leaning towards the bolt-bounce problem. My buffer has no number after the H so I'm going to try an H2 and H3 to see if either of them work. Thanks again. the problems started after some upgrades to the rifle (flash hider, buttstock, Wolff extractor spring, blah blah blah) so just another expample about how sometimes things are better from the factory.
Thanks again. |
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