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Posted: 3/26/2012 8:56:17 AM EDT
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I am the department armorer by default at my agency. I am having some issues with one of our M16s. It is a 14" barreled "Frankengun" with a surplus GI lower to which has been attached a new upper.
The rifle functions fine on semi-auto. A functions check on semi-auto works fine. However, when the selector switch is moved to auto, it will fire one, two, or three rounds with no discernible pattern or repeatability as to the number of rounds fired. The bolt will stop forward with trigger back on a live round. If the rifle is re-charged with the charging handle, one to three rounds can again be fired with the same end result. (This ejects the live round.) Releasing the trigger on auto does not re-set the trigger when this situation is encountered, only recharging the rifle will allow continued fire. Could this be a result of burst FCG parts installed with a Full-auto selector or vice-verse? Or something else? Thanks for the assistance. Mike |
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I also forgot to mention that the burst m16 will have 3 different trigger pulls (light, medium, and gritty/heavy).
Dry fire and then move the bolt back very slow and listen to how the fcg resets. Every 3rd time the bolt is pulled back the fcg will have 2 clicks resetting (this will be the light trigger pull). The auto has the same trigger pull every time and the fcg will never click twice when the bolt is pull back after the hammer falls. |
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Are you sure the hammer is re-cocked and to the rear when the stoppage occurs?
Sounds like the hammer would be forward and you are having an issue with bolt bouce, requiring a heavier buffer. If not bolt bounce, there is something going on with the burst or auto parts. Lets see a picture showing the inside/trigger group area. A burst group would have a burst cam (looks like a gear) and two disconnectors. A full auto group should have a single disconnector. The sear should look the same between the two types of trigger groups... |
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Some questions first:
Does it have an A1 or A2 full length stock or Car Style stock? Do you mean the when it stops the Hammer is in the fired position, ie causing a light primer strike? If so the trigger will also not have reset either. Also someone said to check for two sears, there is only ONE sear in a Full Auto M16. If you have a burst Fire Control Group FCG it will have two disconnectors that sit on top of the trigger. The semi and full auto set up only has one disconnector. The reason I asked about which stock is because with the Car style stock, the regular buffer weight may allow bolt bounce which is one of the symptoms you are detailing fires 1-3 or a few rounds and stops. If that is the case sometimes using a hevier buffer can help fix the problem, example installing an H or H2 buffer. Also check the hammer spring make sure it's not broken, it can also cause problems as you described. |
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Thanks for the replies. It appears that it is a full auto FCG. I hadn't thought of the buffer. I understand that the new "owner" has made some modifications to the rifle since he was issued it so there is not telling what has been done.
I'll try to get some pics posted. Again thanks for the help. (Now I have a "good reason" to be on ARFCOM at work) 
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