AR failure to coming back into battery

[BiscuitsandGravy]

Short of something being loose... I would say under-gassed. But I thought most off-the-shelf AR's are over gassed to run the majority of factory loads. My , Alex.

Where are you ejected cases that cycle landing- 2 o'clock, 3, 4 o'clock?

 

[Vigilant]

What kind of ammo, if you’re sure it’s not undergassd and short stoking? By what kind, I mean WHAT kind, not brass cased, who made it. WWB Walmart ammo has been notoriously underpowered/all over the spectrum?

 

[M67]

Try replacing the buffer spring.

I know, newish AR, shouldn't be the problem, but it might be. I've seen several new ARs develop the issue (one actually being a DPMS), you pull the charging handle back and the thing feels under sprung, bad heat treat or something but the spring is toast after about 50 rounds and doesn't have the force it should have to launch the BCG into battery

 

[halfmileharry]

Since the OP hasn't been back on in 4 days and we've got no new info I'll go with "oil the hell of it for $200 Alex"

 

[brucecrain]

Too heavy of a buffer or get a new buffer spring. Make sure to try different ammo and if none of that work might be a gas tube issue.

 

[Disposable Heart]

Thinking on this...

It's not the buffer. The buffer weight should have marginal impact on the operation of the weapon, mostly to 'time' it and prevent bolt bounce. Too heavy or too light wouldn't cause this issue. Too light would make the gun run fast and feed, but batter the crap out of itself down the line. If you get a misfeed, it would mangle the round trying to shove it into the chamber, often outpacing your magazine spring's ability to feed it up fast enough. Too heavy would not allow enough travel to come back enough, mostly prevent the BCG from coming back far enough.

Not the recoil spring: As the OP stated, if it was the recoil spring, the forward assist would cure this. Too light on the spring (or chinzy), it would not have enough pressure to push the BCG against the normal tolerances of the BCG, round feeding from mag and round going into chamber after snapping over the extractor. It wouldn't go 100% of the way, BUT a quick tap on the FA would remedy the situation (but still require part replacement with new spring)

The Forward assist isn't working. This may lead me to some questions, things to look for without just mindlessly swapping parts and hoping for the best:

Take the BCG out, any scratching where the forward assist is or where the bolt hold open may interact with it? If so, these parts are out of spec.

Does the Forward assist stick out into the bolt carrier group race/tunnel where it might drag?

Check the buffer retainer pin, is it showing any peening, dragging marks or inordinately shiny?

Check the chamber for any burrs or issues, obstructions. Cleaning may not show this and sometimes cheaper barrels can leave the factory without massive QC efforts (looking at you BCA).

Check your extractor and ejector: Take a spent casing and use it to work the extractor and ejector through it's travel. If the round isn't 'snapping' over the extractor into the BCG, it can push it and be out of battery enough. Similar with the ejector: Any issues there can prevent the round from inserting cleanly into the chamber, but may still be engaged by the extractor enough to allow extraction upon misfire.

 

[greed]

Update!!!

I had a chance to go to the range and do some more testing.
- Firing one round manually loaded from magazine results in a successful fire and the bolt locks back on the now empty mag.
- Fired 3-4 rounds in this fashion with same results, checked casing for marks from the ejector and found none. I understand this to mean the gas is not way low or way high.

- Observed several case trajectories as they were ejected and they all left the rifle at about 3 o'clock. I believe this tells me that gas is a little low, but not bad. (2:00 - 2:30) being more ideal.
- Swapped BCG only to another rifle with no change to either rifle.
- Swapped problem rifle upper to working rifle lower and combination fired just fine.


I believe this tells me that the cuprate is in the buffer tube system, either the buffer, spring, or tube. On closer inspection, I notice that the working lower buffer tube is about an inch shorter than the non-working lower buffer tube.



I have not checked the exact lengths, but I assume the longer one is a rifle buffer rather than a carbine buffer.


What do you think? Is this enough to cause the issue? Is there any chance that keeping the same spring and tube, but replacing the buffer to a heavier buffer may fix the issue?

 

[greed]

I found a good site that lists the weights of different buffers.
https://www.wingtactical.com/buyers-guide-for-buffers-buffer-springs/

If I indeed have a rifle buffer tube and buffer looks like the rifle buffer is considerably heavier. Maybe it is causing the bounce without the rifle being high pressured.

 

[M67]

You don't happen to have a 7 position tube do you?

 

[d.kaufman]

You don't happen to have a 7 position tube do you?

I don't think that would matter. I have a strike industries 7 position tube on my daughters ar. It's the same length as milspec 6 position tubes. The notches are just milled closer for finer adjustments.
Now rifle v/s carbine, yeah, that would be a big problem

 

[M67]

I don't think that would matter. I have a strike industries 7 position tube on my daughters ar. It's the same length as milspec 6 position tubes. The notches are just milled closer for finer adjustments.
Now rifle v/s carbine, yeah, that would be a big problem

Some were designed for 308 ARs using a standard 5.56 buffer but with a proprietary spring. Tubes were longer to accommodate the spring

 

[JHB]

Send it back to DPMS let them fix there junk. This is why I won't purchase anything from the Freedom group.

 

[greed]

I did not count the positions, but both the tube and the spring are longer in the lower that causes the issue.

 

[Blakec221]

But why would the forward assist not send it home? I once had a carbine spring and buffer in a rifle length tube. I would have to use the assist to get the first round in but worked fine every round after. I guess I’m missing something here? To me the BCG would have to be catching one something to keep the assist from pushing it the rest of the way in

 

[Disposable Heart]

But why would the forward assist not send it home? I once had a carbine spring and buffer in a rifle length tube. I would have to use the assist to get the first round in but worked fine every round after. I guess I’m missing something here? To me the BCG would have to be catching one something to keep the assist from pushing it the rest of the way in

I'd second this. Even if the buffer was the culprit, the forward assist would still work. But according to the OP, the FA isn't working?

If I remember, DPMS used to have, WAYYY back in the day, some commercial tubes that were a weird length, but I'm talking 'when dinosaurs roamed the earth' kind of way back. If you do have a commercial tube, it might measure funky because it has the weird angle at the end. But using a standard carbine buffer and spring would still work (while not 'milspec' their internal length was milspec length). And all of this STILL doesn't figure out why the FA isn't correcting the bolt issue.

As an experiment, I took the buffer and spring out of one of my ARs and let the bolt come forwards. It, without spring pressure, stopped short of complete closure because there wasn't anything pushing it forwards. I could still use the FA to close the bolt completely. So spring pressure isn't the problem.

 

[Disposable Heart]

It would not be a rifle length buffer tube issue because the OP has 'counted the positions of the tube', and a rifle tube is MUCH longer than an inch, so it's not a rifle length tube.

Greed, did you check any of the things I posted about previously to see if there was anything amok?