Armory Sponsor
Posted: 12/20/2011 2:33:07 AM EDT
|
Just want to know what are the potential reasons which cause auto fire problems in Colt M4 carbine. The rifle works perfect on semi. I checked the auto sear it looks fine and I manually checked it on auto ( I put the selector on Auto and pull and release the charging handle repeatedly, while trigger is pulled, the hammer was dropped every time with the release of charging handle) it works fine. But it does not work when I chamber the bullet.
Any suggestion 
|
|
We need more information. Specifically, what is happening? If selector is on full does the rifle fail to fire on 1st shot? Is hammer not dropping during live fire (though working fine with manual cycling)? 1st shot fine, but 2nd shot fails? Fails halfway through a mag dump? Failure to fire b/c of a failure to eject previous shell - empty shell jamming action? Did you try different ammo? Did you try different mags (ie., getting double live round jam)?
Probably bolt bounce, but flesh this out for us. Sam |
|
Dear Sam, I’ll try to provide the details according to points u raised in ur reply.
1.rifle is firing 1st shot properly and ejected properly. 2. second shot fail ( second shot chambered properly even saw the pin strike on the primer but not fired and when I use that bullet again it goes boom) 3.I tried 2 different ammos. M855 and the second 1 HP Austria (Hirtenberg Austria). 4.yes I tried different mags as well. I hope it helps you understand the condition well. |
|
Starting with easy fixes and do one thing at a time. First, bolt bounce presents as light hits with selector on FA. Consistent 2nd round failure is not typical. Even so, I would try a heavier buffer (not sure what you have now) first. If you have a H, go to an H2 or H3. See if anything changes.
Second, you want to unequivocally rule out an upper problem. If at all possible borrow a duplicate Colt complete upper (with BCG) and try it on your lower. If the duplicate works, you might then swap BCGs and see if you can pinpoint the problem. Similarly, try your complete upper on a borrowed lower. Next up are FCG component issues. Are all your FCG components Colt, and do you know if they are fresh? Springs probably should be replaced regardless, as Tony K wisely suggests, on any "new to you" 16. Like Tony, I strongly advise all Colt parts, BTW. FCG problems can be a bugger to isolate. Marginal hammer spring, marginally out of spec firing pin, bent autosear giving release with inappropriate timing of release......eieio. Hate to admit this, but I've come to the conclusion the best approach is to replace the entire FCG. Yes, this contradicts what I said about doing one thing at a time. Trust me here. The good news is you've got a pony receiver. That means you won't likely have to consider out of spec FCG holes. Burst kit/cam or standard auto? If burst, I would ditch it for standard FA parts. Well, that's a bunch of stuff to do and check. Let us know how it goes. Sam |
|
Quoted:
Hammer is following the BCG. I assumed he had ruled this out from his first post. Rereading it, you may be right. Usmankk, run the autosear test again. Do not simply release the charging handle. Instead, let it down slowly. What we're looking for is the point at which the hammer releases. It should not release until just before the carrier is fully forward. Sam |
|
Mr. Sam first of all I would like to thank you and fxntime for you time and suggestion, now as you suggested to do the autosear test, I’ve done it according to your instructions ( by releasing the charging handle slowly, the hammer drop after the carrier is fully forward ). I am planning to borrow my friends M 16 A1 and I’ll take it to range on this Sunday for upper lower switch trick you mentioned in your previous post.
I’ll inform you guys about it. Once again a lot of THANKS to you |
|
Fxntime's point could still be valid. A marginally weak autosear spring may allow the sear to "float", and fail to engage the hammer when firing. With a more static manual test (even dropping the charging handle) you might not appreciate this.
This is just one of the many reasons a change in all springs is often advised with any "new to you" receiver. Healthy springs are very inexpensive insurance - and will increase the lifespan of FCG parts, too. Sam |
| Reason I'm thinking it's hammer follow is that first shot goes off OK, second round is fed into chamber, hammer follows bolt, you would get the typical light primer strike from the floating firing pin but you'd never notice that the hammer followed the bolt carrier and failed to reset until the bolt locked into place because it's in F/A mode. |
|
Fxntime, Agree, but a marginal hammer spring with the least bit of bolt bounce could mimic this.
Usmankk, A switch of identical uppers/lowers would be more helpful, and results less confusing. But if a 20" A1 is all you have try it. Make sure you try your complete upper on the borrowed rifle lower. You didn't answer my question concerning burst kit? Sam |
|
Quoted:
Quoted:
Sir, its standard auto, I am sorry I skipped this part earlier. By the way I decided to change the FCG components anyway, need 1 more favor from you, please suggest me the best known brand/ company for FCG components. I’ll be grateful Colt. This. Vendors I can recommend include Specialized Armament, Brownells, Dr. Dennis Todd (address and phone can be found over on subguns.com), and Autoweapons.com. Sam |
|
Quoted:
Quoted:
Sir, its standard auto, I am sorry I skipped this part earlier. By the way I decided to change the FCG components anyway, need 1 more favor from you, please suggest me the best known brand/ company for FCG components. I’ll be grateful Colt. I'll second this. Colt FCG is all I run in my RDIAS and all I will use unless I get a Geissele SSF one day. However it sounds like you are experiancing bolt bounce. I run a car buffer in my gun when I'm using subsonic 300 fireball and I forgot to put the H2 back in the gun when I put a 5.56 upper on and I had the same trouble you described. If I were you I'd try a H2 or another heavier buffer and see how things go. Posted Via AR15.Com Mobile |
Armory Sponsor