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Posted: 5/10/2014 5:57:02 AM EDT
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Hello. I have a CMMG complete lower that has run 100% since 2008 or so. Recently I've had some strange problems with the bolt catch after the last round is fired. Sometimes the bolt will lock back and sometimes it won't. Other times the bolt carrier will be locked back but the bolt itself will be extended forward, and not seated back within the carrier. No problems shooting until the last round is out.
These issues occur regardless of magazine or ammo types. Thanks for any help. The thing has me confused is why the carrier would lock back but the bolt would be pushed forward/extended, I have never heard of that before. |
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If the catch is trapping the bolt carrier rather than the bolt, the BCG isn't moving far enough rearward. That's a problem with gas supply, and could be a loose gas key, worn gas rings, or worn gas tube. Could also be low-powered ammo.
The bolt extended forward with the carrier trapped by the catch is normal. Once the bolt rotates out of battery, the cam pin travels rearward trapped the "channel" of the upper receiver, and it doesn't re-seat in the carrier until the bolt returns to battery. HTH. |
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Usually the bolt stays back in the carrier, behind the bolt catch after the last round is fired.
The upper is new from Spikes with less than 200rds in it. The bolt and BCG I got in 2009 or so and has had LOTS of rounds through it. Sometimes though the BCG doesn't get locked back after the last round and the entire assembly is forward in the chamber with an empty mag. What are possible parts that could be causing this? |
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If the rifle is stroking correctly, the ejection distance of the spent case should be 10' to 15' out of the ejection port.
If the spent cases are traveling this far, then suspect something in either the catch, or the mags the problem at hand. If the spent case ejection distance is much less than this, then suspect a gas leak, gas blockage, or binding problem in the rifle, with the short stroking of the action the problem at hand. So on that note, what is the distance of the ejected brass, and at what direction out of the ejection port window. |
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