AR- whats going wrong?

[norman428]

Alright so I recently got my first AR Its used but awesome. So I'm slowly learning all the parts and what can cause issues ect. But one thing I can't figure out is why some of the ammo isn't going off.
Today I went out and fired off about 100 rounds. Out of that 100 about 5 of them wouldn't fire. When looking at the bullet compared to the other ones the "dent" I guess you would call it where the primer was struck was not as big. Is something wrong with my firing pin?
Yes every time this happened i made sure it was locked forward, bullet was in place, everything. I just want to know if this is actually "common" or an issue?
I have no idea of the history of the gun, I'm the third owner the second owner from what I understand never even used it, it was just part of a package deal he bought. So how much the first owner did is unknown.
I did thoroughly have someone who knows about AR's clean it and oil it and show me the whole process, so teats not the issue.
Thanks for the info!

 

[AllenM]

my
More than likely a home trigger job was done and the Hammer spring was modified or changed out with a lighter one. Or mabye installed wrong giving you light primer strikes. Second it could be the firing pin.

I would look at the fire group first though

 

[dukeboy_318]

This to me is an issue, 5% of your rounds are not going of, thats definitely an issue in my book. While I am not an AR "expert" , I do have a lot of experience with them though I do not recall ever having this particular issue. So Id say lets start by checking everything out.
I would check your bolt real good for wear or damage as well as checking your firing pin for damage. Look for burs or dents or scatches, anything that couse hang up the bolt and firing pin.
It could also be a trigger spring or even a trigger issue. check that out and make sure you dont have a relaxed spring or a mis-installed spring.
Also, what ammo were you running? If you were running steel cased rounds, that maybe part of it as some ARs just dont function correctly all the time with steel ammo. You did not say what brand of AR it is, but find out and let us know. Ive got 2 ARs, one will eat anything, the other just does not like steel ammo(WOLF, TULA, Brown Bear etc)

 

[sakima]

Also give the chamber a good cleaning with a chamber brush.

 

[E5RANGER375]

heres what I would check first:

-too much or the wrong lube build up around your firing pin
-weak hammer spring
-backwards hammer spring
-bad firing pin

in the winter time (cold) some lubes will gum up and affect function. not all lube is created equal. Almost everyone either puts too much lube and crap in their AR's or not enough or none of the right stuff on the right parts.

keep us updated with what you find please. i hope its something simple like above. If not, then you get into the more complicated fixes.

 

[M4Madness]

The ammunition could very well be suspect. What brand is it?

Was the hammer falling when you pulled it on the failed rounds? Meaning, did the trigger actually click but the round did not ignite? If the trigger did function, then you were obviously in battery as you should be, and the fault lies in a weak hammer strike or the firing pin itself.

 

[XtremeVel]

If all the above check out, I would look into the ammo. Is the ammo used reloads by chance ? Is so, a primer not fully seated won't always set off the powder. Often times, the first attempt will seat the primer but will give you a light strike.

 

[E5RANGER375]

yes, ammo first, I was assuming he had tried different ammo and ruled that out.

if your shooting wolf ammo, id say you just found your problem.

 

[M4Madness]

When looking at the bullet compared to the other ones the "dent" I guess you would call it where the primer was struck was not as big.

The floating firing pin of an AR-15 will dimple primers when the round is chambered. Therefore, what you are seeing may be the result of chambering, and not from the hammer dropping. My reasoning for asking if the trigger actually functioned is to rule out short stroking.

 

[x10]

E5 gave you your first good post on the problem, I would very much suspect heavy oil in your or dust/dirt/carbon in the bolt and bolt carrier

don't discount other problems and the ammo

good luck

heres what I would check first:

-too much or the wrong lube build up around your firing pin
-weak hammer spring
-backwards hammer spring
-bad firing pin

in the winter time (cold) some lubes will gum up and affect function. not all lube is created equal. Almost everyone either puts too much lube and crap in their AR's or not enough or none of the right stuff on the right parts.

keep us updated with what you find please. i hope its something simple like above. If not, then you get into the more complicated fixes.

 

[dross]

This might be a good spot to ask this question about lube. I've got an AR coming, but haven't used one since about 1991. My last "AR" was an issued M16. We used to just lube the bolt and carrier liberally with breakfree and rock it. What's the current lube best practice for ARs?

 

[M4Madness]

This might be a good spot to ask this question about lube. I've got an AR coming, but haven't used one since about 1991. My last "AR" was an issued M16. We used to just lube the bolt and carrier liberally with breakfree and rock it. What's the current lube best practice for ARs?

I own an M16, and I use Break-Free CLP exclusively, and my rifle runs 100%. To be quite honest, I just spray the crap out of the bolt carrier assembly like you said you were taught in the military and go with it. But, firing a lot of rounds full-auto burns lube off quickly, so I'd probably recommend going a little more sparingly on a semi-auto AR-15. I'd say to just use a light coat on the bolt (including locking lugs) and bolt carrier, making sure to put some on the bolt's gas rings and cam pin surface. Also put a thin coat on the body of the firing pin.

 

[norman428]

So 20 of the rounds were wolf, Flawless. All of the other ones were American Eagle. I guess technically it happened 4 times... I had 5 rounds that I didn't shoot because one of the times it happened when I went to clear it, it tried to double feed and jammed. pain in the a** to get it out when the second round was holding the first one in. So I simply put both rounds with the other issue rounds.
So out of 120 It happened 4 times.
Before going shooting I had my friends dad check it out, help me clean it and oil it, He knows quite a bit about them because he works for the police department and has to do that quite frequently.

The firing pin and bold look to be in good shape. There are signs of wear but no scratches or anything like that.

The trigger assembly seems to function as normal but now that someone has mentioned it, When I had a problem with those rounds, It did seem like the trigger was already back, every time it happened. Would this mean weak spring? How can I check?

Its a rock river ar.

 

[M4Madness]

I had 5 rounds that I didn't shoot because one of the times it happened when I went to clear it, it tried to double feed and jammed. pain in the a** to get it out when the second round was holding the first one in.

Did the trigger "click" and the hammer drop without the rounds firing, or were the instances like the one mentioned above, where the rifle failed to completely chamber a round? If they were simply jams, then I'd suspect the magazine(s). I'd go as far as to say that the majority of failures in an AR-15 rifle are due to junk mags. Stick with USGI aluminum mags (Center Industries, Okay, Aventureline, etc.) or Magpul PMAGs.

Can you elaborate more on the exact details of the 5 failures?

 

[xmas_asn]

I just had a similar problem with a M4 in my Armsroom. If your firing pin parturition is good and so is the headspace you might want to look into replacing your hammer spring. That turned out to be the problem in my case, but in my case it was happening about 5-7th round.

 

[norman428]

I was using a PMAG all day, same one, so the mag should not be the issue. Only one of the times when The round did not fire, did the rifle attempt to chamber a second round without ejecting the first one, when i pulled the handle back to clear the bad round.
so there were really 4 failures, 5 rounds because after i cleared it i choose not to shoot either round that jammed.
The other 3 failures I'm almost certain there was a click, just nothing happened, and if I pulled the trigger again, not even a click, I assume because it was already forward.
Hopefully I'm ordering 500 rounds sometime tomorrow and will have it by next weekend, If I haven't sorted out the problem by then ill be sure to pay alot more attention when it fails to fire.

 

[norman428]

I will also add that most of the time it was the first or second round out of the mag, the rest of the mag was flawless. And I only put 20 in the mag most of the time.

 

[E5RANGER375]

This might be a good spot to ask this question about lube. I've got an AR coming, but haven't used one since about 1991. My last "AR" was an issued M16. We used to just lube the bolt and carrier liberally with breakfree and rock it. What's the current lube best practice for ARs?

This guy is spot on in my opinion!! listen and watch carefully, its all good to go! Showing you a video is much better than trying to type it out I think.


(since it is James, im gonna go ahead and put a language warning on this, lol)
YouTube - AR 15 Lubrication

 

[Thumper]

So 20 of the rounds were wolf, Flawless. All of the other ones were American Eagle. I guess technically it happened 4 times... I had 5 rounds that I didn't shoot because one of the times it happened when I went to clear it, it tried to double feed and jammed. pain in the a** to get it out when the second round was holding the first one in. So I simply put both rounds with the other issue rounds.
So out of 120 It happened 4 times.
Before going shooting I had my friends dad check it out, help me clean it and oil it, He knows quite a bit about them because he works for the police department and has to do that quite frequently.

The firing pin and bold look to be in good shape. There are signs of wear but no scratches or anything like that.

The trigger assembly seems to function as normal but now that someone has mentioned it, When I had a problem with those rounds, It did seem like the trigger was already back, every time it happened. Would this mean weak spring? How can I check?

Its a rock river ar.

Better look at that hammer spring.

 

[M4Madness]

It's hard to tell from his photo if the hammer spring is installed properly or not. The U-shaped loop of the spring should be on the rear of the hammer, as pictured below: