AR diagnosis

AR/M4 AR Technical Discussion
1

Here’s the dealio:

I had had some issues with my AR, and in an effort to diagnose gas issue, mags, etc., today I went to the range and here is a report–

My bolt/BCG was running whistle clean and very wet. I loaded one round into 4 mags. I pulled the trigger, each round went downrange, the bolt locked as it should.

OK. I load several rounds in the mags. Rounds one and two went bang, no trigger pull on the third. No click, no nothing. The bolt was forward, I pulled the charging handle, it ejected a fresh round, chambering a new round. VERY light primer strike.

New mag. First round went bang. The second did not, same as before. Bolt forward. I cycled another round (as it ejected the round, which had a VERY light promer strike), shot the third round, but the same issue with the fourth.

New Pmag. Dame thing: first round went bang, second did not.

I took out my buddy’s BCG and put it in my rifle. Same issue, regardless of mag.

His rifle, no problem, regardless of mag. I ran two nearly full mags in his AR, nary a problem. I did not put my BCG in his AR, which is what I should have done.

I followed up with one round each in four mags, bolt locked back every time.

Same ammo with all mags.

Ideas? Gas issue? Bolt issue? Buffer tube? Trigger/springs? I do not think it is a mag issue or nasty/dry bolt issue.

Thanks, folks.

2

Light Primer Strikes

Any recent FCG work? FCG removed then reinstalled for any reason?

3

A similar thing happened to me a couple if years ago. I put a set of JP reduced weight springs in my stock FCG. Did great until about 1K rounds through the gun. Then the springs started getting weak and I started getting a lot of light primer strikes especially on PMC Bronze. Like Quib said have you dis/reassembled your FCG and is it stock?

4

No, I have not messed with the FCG at all. It is ‘stock’.

5

Are you the first owner?

6

See if the weapon successfully passes a few Function Checks.

[b]FUNCTION CHECK

Test the function of the weapon after assembly, with the magazine removed and weapon cleared, as follows:

  • Cock the weapon; move the selector to “SAFE”; and squeeze the trigger: The hammer should not fall.

  • Move the selector to “FIRE” and squeeze the trigger and hold it to the rear: the hammer should fall.

  • With the trigger still at the rear, cock the weapon: the hammer should not fall. Release the trigger and
    listen for a “Click”. Squeeze the trigger again: the hammer should fall.[/b]

Repeat this Function Check several times. The weapon should not fail any portion of the check.

7

I may be way outta my league here, but is it fully into battery? Try tapping the FA each time, if that does the trick, my guess is your problem is either ammo that’s too weak or maybe a buffer/spring combination that’s too heavy for what you’re shooting.

But I’ll be the first to admit that I’m just pulling that out of my ass.

Odd that it should do it after the 2nd round. Does it have anything to do with which side of the mag it’s feeding from? Instead of loading an even number, load an odd number. and see if you get a light primer strike on the 2nd instead of the 3rd round.

8

jaxman, I am the second owner.

quib, I’ll give it a shot (no pun intended).

complication, good points. I thought it might be the buffer/spring, too, but consensus is taking me to the FCH.

9

sounds like it’s not resetting, or not disconnecting. the function-check quib posted will show it.

one thing to make clearer to the above graphic quib posted- after you let the trigger go, listening for the audible “click” of reset, you should THEN be able to pull the trigger and drop the hammer. the “click” is the reset, which drops the hammer back onto the trigger sear from the disconnect. if you get no click, you’re not resetting… open the weapon and see if the hammer is up or down. it should be down. if you get a click, but can’t drop the hammer- it’s not disconnecting. open the weapon, the hammer will be up.

your “light primer strikes” are most likely just firing-pin bounce dings, and not even strikes.

10

What bkb said. Sorry bud I didn’t mean steer you down the wrong path with my light spring story. Reread your post and I missed the part about not hearing the hammer fall on the trigger pull. That’s what I get for reading posts while I am on the job.

11

What type of front sight base or gas block do you have and is it pinned or clamped properly?

Is your chamber MILSPEC or commercial? What is your buddy’s?

Are you shooting factory ammunition?

12

oops, nm.

13

gas block is pinned properly.

both rifles are mil-spec.

factory ammo.

I will try the function test tomorrow.

14

^^^This;)
And- Is the hammer binding at all. Perhaps it’s tight/dry and the friction from the action reset on the first 2 shots is causing just enough heat to make it stick. I’d dis-mantle the FCG, check tolerances, lube and re-assemble.

15

I did the function check. Pulled the charging handle, rifle on ‘safe’, pulled the trigger, hammer did not fall. Check. Rife on ‘fire’, it fired. Trigger held rear, pulled the charging handle, let the trigger go for reset, trigger does not move–at all. I have to nudge the trigger with my finger each time, but when I do, I hear the reset. Then I pull the trigger and the hammer falls forward. So, aside from the trigger being ‘stuck’ in the rear-most position, all good with the function check.

16

check the trigger for rust, anything else that might be binding it up… check the spring, make sure it’s installed correctly… if all this looks good, replace the trigger spring and try again

eta- i’d probably do the disconnect spring as well. how old is the weapon?

17

Rifle <2 years old. I’ll break it down and give it a good inspection tomorrow.
Thanks for the help.
CM

18

This is also what I was thinking. I had this issue recently with my 10.5" AR. I had 400+ flawless rounds through the gun, then I put my suppressor on it. Ran about 30 rounds through it. After I took the suppressor off it did what yours was doing. After 5 no fires, I opened up the gun and blew into the fire control group and checked to see if the parts were ok. Closed it up and it has worked fine for the last 200 rounds since. My guess was that their was some junk not letting the hammer reset.

Jeremy

19

My wife’s Stag did the same thing. After several hundred rounds, the trigger would no longer reset on its own. It had developed a burr on the disconnector. I had to physically push the trigger forward to reset it. I just replaced the entire fire control group rather than trying to fix the original disconnector because I was afraid it was too soft and other problems would arise down the road.

20

yes the primer will get a small ding even just from being loaded duh to the floating firing pin nature of the AR. Doesnt mean the hammer actually hit it.