Failure to Discharge [AR-15] Bad Ammo or Internal Problem?

[Multifaceted]

PROBLEM SOLVED — Thanks to everyone for their input, very helpful all around.

I searched around and couldn't find any answers specific to my situation.

Let me first preface this by saying the rifle used is a carbine build for my wife, the first one I've ever attempted to assemble. Aero stripped lower with standard JBO LPK. The upper is Wilson Combat 16" carbine length 1:9 w/ M-16 BCG — all bought assembled. I field stripped the upper, cleaned and lubricated it well before shooting it the first time. The lower parts were all lightly cleaned and and the fire control springs lubed with white lithium grease before assembly.

Before the completed upper was acquired, the lower was test fired to test functionality with another Upper and it worked well, ran about 50 or so rounds flawlessly.

About three weeks ago after it was completed, we took the rifle to shoot at her dad's house and ran 60 rounds flawlessly. 30 rounds of Remington 55gr FMJ, and 30 rounds PMC Bronze 55gr FMJ. Went bang every time, no FTF or FTE.

Fast forward to this past Saturday, we took the rifle to the range to get it sighted-in. We eventually got it dialed in pretty well, but the ammo I brought had several duds. I brought three boxes (60 rounds) of Federal XM193 (Plain Brown Box) and a total of 8 were duds. This is some ammo I had just picked up at Walmart that morning. Each of the ejected duds had what seemed to be a good dent in the primer, and didn't appear to be a light strike or anything. In fact the primer strikes look just like the other spent casings of the same ammo.

I also brought a mixed bag of Remington 55gr JHP, Hornady 55gr TAP, and lastly some Wolf 55gr FMJ — and they all fired with no issues... strange.

Out of curiosity, I re-chambered 4 of the eight Federal duds individually with the mag out and was able to discharge two of them. This was kind of a PITA because we did the 30 second wait after each failure to discharge suspecting hang fire.

What would have caused so many rounds to fail to discharge? Is it the fire control group, or perhaps the hammer spring is too light? Could it be the firing pin or the BCG? Or perhaps was it just the ammo (XM193)?

I've been shooting for many years, have owned an shot AR-15s for quite a while now and haven't com across this issue. Also, I am by no means an expert.

 

[raider80]

Do they look like light strikes? I had this problem a few months ago after I polished the trigger. I accidentally put hammer spring in wrong and got a few light strikes.

 

[Multifaceted]

Do they look like light strikes? I had this problem a few months ago after I polished the trigger. I accidentally put hammer spring in wrong and got a few light strikes.

None that I could tell. I compared them to some spent brass from the same boxes and they looked similar.

 

[Boom Boom]

Grease on the firing pin would do it.

 

[Multifaceted]

Grease on the firing pin would do it.

Hmmm, I do grease the locking lugs but keep it off of the bolt face. But I'll look again later when I clean it. I didn't clean it from the last 60 rounds ran before the range on Sat; however, I did remove the BCG to add oil before we left... maybe some accidentally got smeared on the bolt face when inserted it into the receiver...

 

[DraKhen99]

I know it's not *really* related, but I had the same thing happen to some Lake City .45 ACP pistol ammo that I bought. In each box of 50, one or two wouldn't go bang on the first pull, so I'd eject them, and at the end of the magazine, I'd drop that sucker in and pull the trigger again - every time they went bang. I'm curious as to what causes this.

-John

 

[Boom Boom]

If grease or heavy oil gets into the firing pin area, it will cause misfires. It slows down the firing pin and gets worse after firing shots since powder residue tends to collect in there and really gums things up.

 

[Multifaceted]

If grease or heavy oil gets into the firing pin area, it will cause misfires. It slows down the firing pin and gets worse after firing shots since powder residue tends to collect in there and really gums things up.

I'll keep that in mind. What's odd is the mixed bag of ammo were all fired last, after the three suspect boxes were expended, and all of the mixed ammo fired without problem. It was approximately 25-30 rounds of Remington, Hornady, and Wolf.

 

[rwbow1969]

Too much lube probably. I run mine close to dry, just a light hint of lube. I don't use grease of any kind in mine, grease collects too much crap. Thousands of rounds and not one problem.

 

[jimbobborg]

The ammo with the problems have harder primers. The same with DraKhen99's Lake City ammunition. If the hammer doesn't have enough oomph you'll get the dent in the primer but no boom. You need at least a 4 pound trigger to set the mil-spec primers off.

 

[Multifaceted]

Too much lube probably. I run mine close to dry, just a light hint of lube. I don't use grease of any kind in mine, grease collects too much crap. Thousands of rounds and not one problem.

I used to run mine somewhat drier than now, but had been lambasted (not really, but politely criticized) here for it, so I've converted to using synthetic oil and red bearing grease, and rather like it. Since implementation, no problems in my rifle or the new one until that ammo was used...

The ammo with the problems have harder primers. The same with DraKhen99's Lake City ammunition. If the hammer doesn't have enough oomph you'll get the dent in the primer but no boom. You need at least a 4 pound trigger to set the mil-spec primers off.

Interesting, but do you mean the trigger spring or is it the hammer spring that needs to be heavier?

 

[Pinecone]

Hammer spring is what counts.

Mil spec ammo has a harder primer than some commercial ammo.

It could also be quality control on the ammo.

Or a combination of things. Light hammer spring, hard primers, a bit of grease on the firing pin.

 

[Multifaceted]

Hammer spring is what counts.

Mil spec ammo has a harder primer than some commercial ammo.

It could also be quality control on the ammo.

Or a combination of things. Light hammer spring, hard primers, a bit of grease on the firing pin.

Yes, that's how I understand it as well, but he wrote at least a 4lb trigger... So, I was just clarifying on which spring (or both).

Everything has been noted, I suppose I need to reassess and return for some more function check.

 

[Flipz]

Are you sure you installed the hammer spring in its correct orientation? If installed backwards it may still have enough power to ignite non-military primers but not enough for harder military primers.

 

[Multifaceted]

Are you sure you installed the hammer spring in its correct orientation? If installed backwards it may still have enough power to ignite non-military primers but not enough for harder military primers.

I'm pretty sure, but I don't doubt myself that I might have done it wrong either... especially since this was my first assembly. However, all prior live function tests ran without error. I'll check again later when I clean it just to be sure.

Thanks everyone for the replies so far, looks like I've got a couple of items to cross off.

1.) lighten the lube, sans grease
2.) confirm correct hammer spring installation

I haven't any more XM193 to run it against, but I will check everything again and use process of elimination. It starting to look as if it is the light hammer spring on hard mil-spec primers. I typically don't use much mil-spec ammo in AR-15s. No reason, I just don't buy it much.

 

[ObsceneJesster]

First thing I'd do is strip the upper down and remove all of the grease. It's really not necessary and can contribute to failures. Especially in cold weather.

Strip down the BCG and clean it up good. When you put it back together, only apply a very light amount of lubrication to the firing pin. Too much lubrication in there (especially grease) can cause a suction effect which contributes to light strikes.

When you re-assemble the upper, make sure you only use lube. Apply a good amount to the carrier grooves and on the side of the carrier. Just use a little bit on the bolt lugs and make sure you don't get it down into the bolt face. Lastly, add some lube to the Charging Handle and then work the action a few times.

If you're still getting misfires after removing all of the grease then you can start diagnosing other possible issues.

 

[wilcam47]

Bad primers in the ammo lot?...while the grease could be the problem it doesn't sound like the duds were the first out of the box...they were randomly spread out in the 60rds...nothing wrong with cleaning out the grease. Dry BCG is bad too IMO... Id try changing ammo first.

 

[annihilation-time]

I only use Slip 2000 EWL. No grease.

 

[Multifaceted]

First thing I'd do is strip the upper down and remove all of the grease. It's really not necessary and can contribute to failures. Especially in cold weather.

Strip down the BCG and clean it up good. When you put it back together, only apply a very light amount of lubrication to the firing pin. Too much lubrication in there (especially grease) can cause a suction effect which contributes to light strikes.

When you re-assemble the upper, make sure you only use lube. Apply a good amount to the carrier grooves and on the side of the carrier. Just use a little bit on the bolt lugs and make sure you don't get it down into the bolt face. Lastly, add some lube to the Charging Handle and then work the action a few times.

If you're still getting misfires after removing all of the grease then you can start diagnosing other possible issues.

It was pretty cold and breezy that day, about 36°. Yeah, the grease is something new that I've been experimenting with, no real issues over the summer in my 20" Bushy, but maybe that is just dumb luck. I'll leave the grease out going forward until I've eliminated all of the problems. Thanks!

Bad primers in the ammo lot?...while the grease could be the problem it doesn't sound like the duds were the first out of the box...they were randomly spread out in the 60rds...nothing wrong with cleaning out the grease. Dry BCG is bad too IMO... Id try changing ammo first.

Perhaps, I don't know for certain, the dents appeared to be the same as from the spent brass. I probably should have kept the "duds" for pics to post - but instead just dropped them into the misfired can at the range.

Yes, they were all sporadic from all three boxes. I fired a mixed lot of Remington, PMC, and Wolf .223 last afterwards and they all fired without problem. Like others have suggested, I ought to confirm correct hammer spring installation in case it is not being released with full force for the mil-spec primers of the XM193.

 

[wilcam47]

It was pretty cold and breezy that day, about 36°. Yeah, the grease is something new that I've been experimenting with, no real issues over the summer in my 20" Bushy, but maybe that is just dumb luck. I'll leave the grease out going forward until I've eliminated all of the problems. Thanks!



Perhaps, I don't know for certain, the dents appeared to be the same as from the spent brass. I probably should have kept the "duds" for pics to post - but instead just dropped them into the misfired can at the range.

Yes, they were all sporadic from all three boxes. I fired a mixed lot of Remington, PMC, and Wolf .223 last afterwards and they all fired without problem. Like others have suggested, I ought to confirm correct hammer spring installation in case it is not being released with full force for the mil-spec primers of the XM193.

well the way I look at it...is if the first 5 or 6 had a problem firing I would suspect grease...as the gun is still relatively cold...BUT since it was sporadic I say bad primers/ammo...just my thoughts..