Help troubleshooting causes of a malfunction

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CopperFouling

CopperFouling

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I am having some issues with my rifle malfunctioning. I have some ideas about what could be causing the malfunctions but wanted to see what people here think are the highest-probability issues since I am much more knowledgeable about handguns and shotguns than I am about rifles.

Here's the context. I have a Daniel Defense DDM4V7. The bolt carrier group is coated in NP3+. I had 100 rounds of 55-grain 5.56 NATO through it (PMC, if I recall correctly). Those 100 rounds had no malfunctions.

Recently, I returned to the range to zero it with 77-grain 5.56 NATO made by IMI (same as listed here: https://www.midwayusa.com/product/2090124928). I bought that particular load because it is supposed to be highly accurate from a 1:7 twist barrel and it has a good BC. However, it is not cheap ammunition.

After roughly eight shots, the BCG cycled backward, but it failed to cycle all the way forward and go into battery. It was stuck well short of the chambered round. And the BCG was really, really stuck. I had to collapse the stock and tap the stock firmly on the ground to get the BCG to move rearward.

Figuring that I had perhaps had an out-of-spec round, I chambered another round and fired. The BCG cycled rearward again and failed to go into battery exactly like the previous malfunction. I cleared it in the same way.

I can think of a handful of possible causes:

1. Possible: The ammunition is out of spec.
2. Possible: The ammunition does not cycle well in my rifle.
3. Possible: The NP3+ coating on the BCG is causing the malfunctions.
4. Unlikely: The magazine is causing the malfunctions. I rate this as unlikely because the magazine is a barely used Magpul.

My first thought is to swap the ammunition first and see if I experience the malfunction again.

My second thought is to keep the ammunition the same and swap the BCG.

I figured, though, since I am not experienced with rifles like others on here, that I would see if anyone has ideas on the cause. Any troubleshooting advice is appreciated.
 
Does the bolt carrier move freely back and forth with an empty gun? Could the buffer detent have come loose or possibly be too long? Any obvious damage inside the receiver? Is something weird in the trigger group? Is the charging handle in good shape and moving freely? Did you try a different magazine? Have you shot it with 55 grain ammo after you started having problems?
 
First thing I would check, would be to put 1 round in a mag, fire and check to ensure it ejects cleanly and the bolt locks open on empty. If the round ejects in a strange direction or weakly, or the bolt fails to lock, or locks by the carrier rather than the bolt face, it could be a short-stroking issue.

Also, make sure the BCG is clean, and well lubricated with thin oil or CLP.

(I had my 20" .308 out over the weekend, and in the cold temps, it stovepiped the first 2 rounds. I went to oil the bolt with my usual Mpro7, the bottle didn't slosh when shaken. I cleaned the bolt up and relubed with CLP and it ran without a hiccup the rest of the day. Seems tightly machined BCG's with low round counts can be kinda picky about lubrication. Just anecdotal tale that MAY be relevant?)
 
1KPerDay said:
Does the bolt carrier move freely back and forth with an empty gun? Could the buffer detent have come loose or possibly be too long? Any obvious damage inside the receiver? Is something weird in the trigger group? Is the charging handle in good shape and moving freely?
Click to expand...

I can take a look tonight.

1KPerDay said:
Did you try a different magazine? Have you shot it with 55 grain ammo after you started having problems?
Click to expand...

No, I have not. I did not have any of the 55-grain rounds with me that day. If my visual inspection doesn't find anything, I think that changing back to the 55-grain rounds will be my first step troubleshooting.

Driftertank said:
First thing I would check, would be to put 1 round in a mag, fire and check to ensure it ejects cleanly and the bolt locks open on empty. If the round ejects in a strange direction or weakly, or the bolt fails to lock, or locks by the carrier rather than the bolt face, it could be a short-stroking issue.
Click to expand...

I can do that the next time I am at the range.

Driftertank said:
Also, make sure the BCG is clean, and well lubricated with thin oil or CLP.
Click to expand...

Now that I do know. I had the bolt lubricated well but not to the point that oil was running down it. I am using Breakthrough, which has worked well for me for several years.
 
CapnMac said:
Hinge it open and eyeball the buffer detent pin. If it's crooked or bent, it could be "grabbing" the slot in the bottom of the BCG.
Click to expand...

Is the buffer detent pin just a different term for "retainer" as used here around 1:08?

 
Last edited:
@1KPerDay, the BCG and charging handle appear to cycle fine. I loaded a Snap Cap from a magazine today into a empty chamber, cycled the BCG, and ejected the Snap Cap. The second Snap Cap loaded fine. I didn't feel any binding or anything.
 
You left out the most interesting part.
CopperFouling said:
. . . failed to cycle all the way forward and go into battery. It was stuck well short of the chambered round.
Click to expand...
What do those two rounds look like? Do they chamber freely? Are they marked up?

It almost certainly NOT the BCG, and not the magazine. It's likely a tight chamber and slightly oversized ammo, and less likely a hangup in the action. Without a report on the two rounds that FtRB (Failed to Return to Battery), there's no way too know.
 
I also want to know if those two rounds even fit in the chamber. Where was the BCG at exactly?

I have seen oversized rounds in factory ammo before. For example a Winchester White Box .40 that literally wasn't even close to fitting into the chamber of my Sig. I mean not even close. Or some Pakistani 7.62 NATO that wouldn't fit in my M1A.
 
edwardware said:
You left out the most interesting part.

What do those two rounds look like? Do they chamber freely? Are they marked up?
Click to expand...

To be honest, I don't recall, since this happened a number of weeks ago. I did not have any trouble extracting them from the chamber by hand. I wish I had taken pictures. If it happens again, I will.
 
Andrewsky said:
I also want to know if those two rounds even fit in the chamber. Where was the BCG at exactly?
Click to expand...

I wish I had a picture of the position. If I recall correctly, the BCG was probably a quarter to half inch away from properly closing. It wasn't a subtle gap.
 
Make sure a primer didn't fall into the trigger group. It can cause the hammer to stay partially up and not let the bolt move. I had this happen on a pd hunt.
 
I had a similar problem with a new Ruger 5.56. Ended up being the tiny keeper clip for the firing pin retainer was installed wrong. When it vibrated around to the right spot it jammed the bolt.
 
the suggestions are a good place to start.if all is ok I would have to think it might be a low power load with your ammo just a suggestion
 
No idea about the specs of your ammo, but we needed to use heavier buffers on our guns using Black Hills 77 grain MK262 ammo. H2 as I recall.
 
deputy bruce said:
the suggestions are a good place to start.if all is ok I would have to think it might be a low power load with your ammo just a suggestion
Click to expand...

That particular round is not low power. 77 grains at 2740 FPS.

FL-NC said:
No idea about the specs of your ammo, but we needed to use heavier buffers on our guns using Black Hills 77 grain MK262 ammo. H2 as I recall.
Click to expand...

That is excellent information. The IMI round is basically a duplicate of the MK 262 (I was looking for that load when I bought it, and Black Hills wasn’t available at the time). I wonder if that could be it.
 
Check for a case neck stuck in the chamber neck. I had the same thing happen with a new AR, though I looked at the chamber after one round, because I have seen it happen before.
If that is the case, time to head to the gunsmith. It's not a fun job.
 
this is a curious situation if your description is accurate. please let us know what you figure out.

normally when people describe something similar, it's an obstruction in the chamber or an out of spec round but
in your description, you shot 8 rounds, then had a stoppage. you loaded another round and fired it, then had a second stoppage. the fact that you loaded a round between the stoppages indicates the chamber itself is not obstructed, and i would think neither is the trigger group or BCG.

i've fired a lot of rounds through a lot of ARs over the past 30 years and never heard of the buffer retaining pin causing issues, but i could see conceptually how it might in this situation, but it really doesn't match the description of your clearing the malfunction. if it was in a position preventing the BCG from going forward, it wouldn't make it hard to go backwards. and then do the same thing the next time. it would also be easy to diagnose as it should exhibit the symptom when cycling by hand.

low power ammo (unlikely from IMI) would cause short stroking, where the bcg goes back, but fails to pick up a round, then closes on an empty chamber. or.. sometimes grabs the round in the middle and sends it forward nose up or something.

almost all malfunctions are MEAL: magazines, extraction, ammo, lube
the problem isn't extraction. and you said you lubed it. that leaves magazines and ammo. it's possible you got some bad ammo. inspect the rest of your rounds. but if your gun doesn't run on 77g IMI, i'd expect DD to make it right. As good as pmags generally are, the first step i'd take troubleshooting would be to try another mag.

it's generally a good practice to make a mark on your mag when you have a malfunction. that pmag would have two marks on it now. if you find all your mags in your rotation are clean but one has a bunch of marks on it, get rid of it.

my second best guess would be a popped primer floating around somewhere in the action. if that's the case, make sure you check the tip of your firing pin and make sure it's not eroded. root cause could be a tight chamber.
 
So I was planning to head to the range with some different ammunition and magazines on Friday, but a family member of mine took a trip to the hospital (everything is fine now).

Right now, my plan is to
  • Check the buffer retaining pin
  • Swap ammunition
  • Swap magazines
If I have the malfunction again, I will mark the magazine, take pictures, and take better notes.

taliv said:
almost all malfunctions are MEAL: magazines, extraction, ammo, lube
the problem isn't extraction. and you said you lubed it. that leaves magazines and ammo. it's possible you got some bad ammo. inspect the rest of your rounds. but if your gun doesn't run on 77g IMI, i'd expect DD to make it right. As good as pmags generally are, the first step i'd take troubleshooting would be to try another mag.

my second best guess would be a popped primer floating around somewhere in the action. if that's the case, make sure you check the tip of your firing pin and make sure it's not eroded. root cause could be a tight chamber.
Click to expand...

Thanks. I will check those for sure.

It had enough lubricant on it that I had to wipe my hands thoroughly when I handled the bolt last week. Lubricant wasn’t dripping from the BGC, but it should have been sufficient.

I don’t expect DD to cover it under warranty since I coated the BGC. That one’s on me. I should have known better than to fix something that wasn’t broke. Then again, I may buy a backup BCG and see if I can duplicate the problem. That’s expensive, though, so retainer inspection, ammunition, and magazines will be my first steps.
 
I finally had time to go to the range today. The malfunctions continued.

Here is a picture of the BCG jammed short of going into battery.

4B11095D-917C-4428-A2F5-E02722881B88.jpeg

I was unable to determine the cause, but I have determined the following:

Before shooting, I made sure to oil the BCG, especially the cam pin, bolt, and rails on the underside of the BCG. It is likely not a lack of lubrication.

I had the same issue after switching ammunition to American Eagle 55-grain 5.56. I also noted that the rounds that chambered when the BCG jammed again were not dented, smashed, or visibly damaged. It is likely not the ammunition.

I had the same issue with two Magpul Pmags. It is likely not the magazines.

I did note that the bolt was kind of hard to pull forward prior to reassembly. When I closed it last, it seemed stuck in the forward position.

At this point, I am thinking of swapping the BCG.
 
Some rounds chamber and fire fine and others don’t?
If you load a full mag and manually cycle the action by pulling the charging handle and letting it go, 30 times, how many malfunctions do you get?
 
That sounds identical to the problem I had with the Ruger.
Part #14 in the pic below is the fire pin retainer. On the Ruger, this can be installed improperly and cause the bolt to stiffen or lock up intermittently.
.
Screenshot_20211231-233529_Google.jpg
 
When was the last time you removed the carbon build up in the BCG. This along can cause malfunctions that you described. A neighbor bought a AR very very cheap because it was doing the same thing. The gas chamber was totally carboned up. I have the Otis tools for removing this. It took hours to break all of the carbon out. Once cleaned, rings oiled all was good.
 
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