I have an AR with strange issue

[Fallbackpuppet]

Is the hammer spring installed correctly?

While I am totally capable of making mistakes of that nature (and I will check). I find it unlikely because the gun worked fine for several years, I have had a couple of triggers in and out of the lower several times and the odds of doing it wrong repeatedly (and mine working after reinstalling the trigger) is very low. So far I think the most likely cause is the recoil spring isn't quite putting the bolt back in battery.

 

[JEVapa]

What kind of ammo? Where'd the recoil spring come from? Also, Next time, if you get a next time before you change anything, after the second round chambers, hit the forward assist and then shoot it. If it fires, then your spring may be dead. Check the bolt for any deformations and your chambers for little pieces of FOD just in case.

You can also put her gun's lower on your upper and see if it does the same thing, just to see if you can isolate the offender.
Also, does it do it everytime it is fired? Or everytime she fires it?

 

[GHArms]

If the hammer is dropping on the pin and the firing pin fails to ignite the SECOND primer (you said it fires first round), the bolt is not fully in battery. Look on the primers in which were in the chamber when the hammer dropped (second round as you said). Is there is slight little dent? If no, its way out of battery. If yes, then probably not in far enough to get ignition. Clean chamber and bolt and if that doesn't work, try stronger hammer spring and/or buffer spring. Sometimes Wolf/Tula ammo is really tough to ignite in my x39 rifles.

 

[Fallbackpuppet]

What kind of ammo? Where'd the recoil spring come from? Also, Next time, if you get a next time before you change anything, after the second round chambers, hit the forward assist and then shoot it. If it fires, then your spring may be dead. Check the bolt for any deformations and your chambers for little pieces of FOD just in case.

You can also put her gun's lower on your upper and see if it does the same thing, just to see if you can isolate the offender.
Also, does it do it everytime it is fired? Or everytime she fires it?

Good ideas, we are shooting PMC x-Tac 5.56 NATO 62gr Green Tip. I have put her upper on my lower and it works fine, my upper has the same issue when connected to her lower. It does the same thing every time it is fired and it doesn't matter who is firing it.

 

[Fallbackpuppet]

If the hammer is dropping on the pin and the firing pin fails to ignite the SECOND primer (you said it fires first round), the bolt is not fully in battery. Look on the primers in which were in the chamber when the hammer dropped (second round as you said). Is there is slight little dent? If no, its way out of battery. If yes, then probably not in far enough to get ignition. Clean chamber and bolt and if that doesn't work, try stronger hammer spring and/or buffer spring. Sometimes Wolf/Tula ammo is really tough to ignite in my x39 rifles.

Shooting PMC x-Tac 5.56 NATO 62gr Green Tip, and there is a very slight impression on the second primer. Also the bolt looks to be fully in battery after the first round. I am going to change out the recoil spring and see if that helps.

 

[JEVapa]

my upper has the same issue when connected to her lower.

Change the spring with a new one. (a good new one). If you have an H buffer, replace it with a standard buffer.

 

[GlockPride]

Likely bet could be the buffer spring. However, I’ve also have buffers “explode” or come apart in the tube. Might not hurt to pick up a fresh one of those as well while you’re grabbing a spring. Good insurance to have even if you don’t need it right at this moment.

 

[Shadowrider]

In my experience using a light JP hammer spring, I had to chop the tail on a mil spec hammer to get consistent ignition. You could just have a weak hammer spring but that doesn't make much sense with you swapping things around and it working.

I'd confirm the OOB possibility first, then change the hammer spring, then look at the holes in the lower in that order.

 

[scott024]

If the hammer is dropping on the pin and the firing pin fails to ignite the SECOND primer (you said it fires first round), the bolt is not fully in battery. Look on the primers in which were in the chamber when the hammer dropped (second round as you said). Is there is slight little dent? If no, its way out of battery. If yes, then probably not in far enough to get ignition. Clean chamber and bolt and if that doesn't work, try stronger hammer spring and/or buffer spring. Sometimes Wolf/Tula ammo is really tough to ignite in my x39 rifles.

I agree with the bolt not being fully in battery. Dirty chamber/upper or needs lubed. My suppressed 300 BLK gets dirty fast, and I use it a lot so it doesn't always get cleaned after every outing. It has done the same thing, goes click on the second round, sometimes third round. After recharging, that's when I check and usually the bolt isn't fully engage.

 

[Snattlerake]

A gun is a mechanical thing. I love troubleshooting mechanical things. Especially when you have a known good gun right next to you. It seems that you have narrowed down most of the possibilities by swapping known good working parts from one gun to the other and following the problem using those parts. It is very fortunate the problem does follow the parts and is not an intermittent problem.

I would have had to have a chart made as to what parts I swapped, what the results were, and what parts were replaced. Because of CRS.