I am a newbie to the world of the AR. Just built a kit and wanted some input on the following problem.

I recently built a kit and am having trouble. It has been firing just fine as I have put about 300 rounds into paper with it this week. Today after about 100 rounds it would let me charge the first round into it... pull trigger... BLAM... guns cycles with new round in chamber but the hammer did not cock back into firing position. Pull charging handle ejecting round let it slam shut...BLAM...next round does the same thing hammer not cocked. Every round I charge shoots every round gun cycles does not. Rounds that dont fire are ejected by me and all have a very light firing pin dent on primer I beilieve from the hammer following the bolt back into position. I can tell the rear of the firing pin is getting trashed from the hammer rubbing on it as the gun cycles back and then forward but the hammer does not stay down in position to fire and grinds against it as it wants to stand up in fired position.

SOOO I havent had time to get in there and have a look around. I looked over the upper but then on my way home I thought the whole thing over and relized it must be in the lower. The shell ejects fine from the round that fired. Some input would be great.

Thanks Lee

Could be short stroking. The bolt carrier not going back far enough to not cock the hammer. Sear could also be not catching the hammer hook.

sounds like short cycling to me.  The indent on the primer is normal in an AR due to the free floating firing pin.  Start with the easist first, what kind of ammo are you using?  If it's good quality ammo then you need to investigate the buffer and the gas system as culprits.  I'm also a bit concerned about this "grinding" you describe.  I doubt if you're hearing some kind of grinding it has anything to do with the hammer rubbing the back of the firing pin.  Was this rifle well cleaned and well lubed?  If not, take care of that first, this is very important for AR's.

Mike

I took the gun to range again today and made a new discovery into my problem.

The hammer is getting hung up on the upper hook of the dissconnector. This happens every time I fire the gun. I then have to push the trigger forward with my finger to get the dissconnector to let the hammer into cocked and ready to fire position.

Any solutions without taking a dremel tool to the dissconnector or hammer to remove these hooks?

Out of the USMC manual:

1) weak or broken action spring

2) unlubricated or dirty action spring and receiver extension(buffer tube)

3) improper gap space or worn, missing, or broken bolt rings

******This is what I would check first. Look at your bolt rings----are they lined up together. THE GAPS SHOULD NOT ALIGN, at least not all three. This will cause short stroking and is very eay to fix. Also, did you put the rings on the bolt?. If so you might have bent one. Just a thought.

4) gas leakage caused by broken or loose gas tube around front sight base.

*****This I'd check third

5) improper alignment of gas tube and carrier key

Also consider that if you built it yourself the trigger group may not have been assembled in the correct fashion(ie correct order with springs in proper places) and this might result in hammer not striking with enough force. Hammer springs should sit on TOP of the trigger pin, for instance.What did you use as a reference to build it?
***********************This is what I'd check second. I've got a feeling this is it, though, given that you have to push the trigger forward to get the trigger/hammer to function.

Are you sure you put the disconnector spring into the trigger before placing disconnector in?

Does the hammer go forward? are you sure? Hammer catching on the disconnector is normal provided it lets go at end of trigger second stage.

What kind of mags are you using?

One more question: Where did you get your parts/kit?

Thanks for the replies to my post I appreciate it.

I followed the USMC Manual and the Artical from this sight on building your lower stripped reciever. Today I checked all internal parts and they are in the correct order.

The kit is from J&T.  It shoots fine and does not act like short stroking. Today the first 20 or so rounds would hang up on the hammer / dissconector upper hook. I dont think I have a two stage trigger but, I AM A NEWBIE. (troll to most AR15 members).

When I push the trigger forward a little it lets go of the hammer then I can fire. Next round hangs up on the second stage hook on the dissconnector (if it is a second stage hook).

What manufacture receivers, etc. If its not short stroking then you've got a problem with your trigger group--something is not matching up properly. But then why would it function when you manually feed?

Shoot it with only 1 round in the chamber and no mag. Then open the receiver. Where is the hammer? Back or forward? Sounds like you are saying it is forward.

I'd think about taking the trigger/hammer group out and re-assembling as per USMC manual. Don't take shortcuts--do it by the numbers. But first check your disconnector spring that sits in the trigger. Does your Disconnector wiggle feely when you press on it. It shouldn't. there should be some resistance from the spring.

It may be that your parts kit doesn't match up with your receiver properly. One reason I stick with the "name brand parts".

I'm thinking that if it operates properly when working action manually then it just about has to be short stroking. Does the bolt lock back after the final round?

If you have the USMC manual go to page 3-6. let me know.

You're on the right track, Mzzlebrk. I just put 5 JT kits together couple months ago and in one of the lower kits the disconnector was just a little tight when mating with the hammer. You could either polish a little with 600 grit sandpaper or a stroke or two with a file on the end of the disconnector, right at the tip where the hammer engages when fully retracted. To make sure this is it just take the lower and pull back the trigger like you were firing it with the hammer already in the fired position. Then push the hammer fully down and release. Next release the trigger slow and you will probably find that it is hanging up. This might even break in if you fire it a few more times.

ARjunky

What ARjunky explained is exactly it! J&T suggested maybe I put the wrong spring under the dissconnector and it is pushing forward too much and hanging up on the hammer.

The bolt locks open after last round. Never a dull moment there.

Why then is the hammer and dissconnector built with that second stage (extra stuff??) built into it? It would seem if those two areas were ground down to nothing the weapon would have no problem at all.

Can somebody explain the neccesity of the extra need for this potential hangup?


I am beating myself to DEATH over this

I don't know for sure, but I think it keeps the trigger and the hammer from rebounding to fast and beating the surfaces excessively. You can't release the trigger fast enough not to catch the disconnector. When the disconnector is released it only jumps a short distance before it is engaged again for the next shot, instead of the momentum it would have if there wasn't one. If the disconnector is removed the trigger will not catch the hammer either.

ARjunky

The trigger works in a "2 stage process" so that it can't run full auto. When you pull the trigger the rifle fires and when the carrier rides back it cocks the hammer back. If you are still pulling on the trigger when this happens the hammer would follow the carrier forward except that the disconnector hook catches the hammer and holds it in the cocked position. Then, an instant later when you let go of the trigger the disconnector releases the hammer and it moves forward slightly onto the sear surface.

All semi auto firearms must have some sort of trigger disconnector mechanism because you cannot release the trigger fast enough.