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Posted: 12/2/2014 11:43:18 PM EDT
| I have a colt lower that is full auto. This is a department owned weapon. It has a 10.5 radical firearms upper on it. The gun cycles fine on semi auto but will not cycle on full auto. I had a carbine buffer in it and thought that was the problem so I put a h2 buffer in it and thought that would fix the cycling issue. But it is still only firing one round. Any ideas what the issue is? |
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Quoted: Quoted: The bolt carrier is the one out of the m16. And yes it fired full auto prior to putting a new upper on it. Sounds to me like the gas port may be too small or the gas block is not aligned perfectly causing it to short stroke. Who built the upper? |
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you should check the gas port size. stock uppers are not always gassed to run full auto. even if it locks back and cycle fine and semi, it can choke on full auto.
the fact that it cycles on semi indicates that there should not be an issue with any of the parts as long as it is a m16 profile carrier and select fire parts kit. if it is carbine length upper with a 10-12 inch barrel it should be gassed in the mid to uppers .070s |
| Is the sear releasing the hammer or does it fire in "semi" when it is supposed to be on auto? If the hammer is released, it could be that the bolt is bouncing and a new buffer/spring combo is in order. Get it, unload it, and hold the trigger while cycling by hand (don't worry about completely releasing the CH as if you were actually loading a live round... more like you were clearing the rifle) to see if it functions in auto. If it does function like that I would bet on bolt bounce but if it doesn't, it might be something where the BCG engages the sear (In this case, I would try a new carrier maybe but I have never seen that happen in my limited experience). I'm not the autoweapons master around here but this is the best check based on my experience. |
| Chances are, the LPK is a semi only kit. Same deal with our Dept (DHS) M4s; they were "hand-me-downs" from the BP and the full auto innards (a simple roll pin replaces the sear pin) were removed and semi innards installed, along with tan painted selectors to tell the Firearms guys which ones have the "Fun Switches" and which ones don't. |
| I should've done a better job at describing everything. It functions fine on semi as stated before. On full auto sometimes it will fire two rounds before not firing again. Most of the time it fires one shot on full auto and it will chamber another round but not go into battery. I then have to eject the round and chamber another one. |
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Quoted: I should've done a better job at describing everything. It functions fine on semi as stated before. On full auto sometimes it will fire two rounds before not firing again. Most of the time it fires one shot on full auto and it will chamber another round but not go into battery. I then have to eject the round and chamber another one. It seems odd that your only experiencing the problem on full auto. |
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Quoted:
Chances are, the LPK is a semi only kit. Same deal with our Dept (DHS) M4s; they were "hand-me-downs" from the BP and the full auto innards (a simple roll pin replaces the sear pin) were removed and semi innards installed, along with tan painted selectors to tell the Firearms guys which ones have the "Fun Switches" and which ones don't. It has functioned on auto previously... from my understanding, no lower parts have been switched... just the upper. Quoted:
Quoted:
I should've done a better job at describing everything. It functions fine on semi as stated before. On full auto sometimes it will fire two rounds before not firing again. Most of the time it fires one shot on full auto and it will chamber another round but not go into battery. I then have to eject the round and chamber another one. It seems odd that your only experiencing the problem on full auto. This is why bolt bounce came to mind. A worn out or underpowered spring could easily be the culprit. |
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Quoted:
An H2 should have corrected bolt bounce. I wish I could take it to the range, problems are easier to diagnose when your on the range with your box of spare parts. I agree... i would have thought that would help out too. I agree that the spring is the next thing to look at. The sear seems to be working fine since it looks like he is having to recharge the rifle to fire it, and if it wasn't catching at all I think he would likely have had it kinda runaway on him by now. |
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Agreed. If it's chambering the next round, it's not a short stroke or a gas issue. Sounds like bolt bounce, though you're right, I would have expected the h2 to correct it. And if it's functioning well in semi, that strengthens that position.
Best to get it to a range and tinker with it. |
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