DPMS AR15 Ejecting but not picking up next round

homeslice · Jan 3, 2017

Hey guys - I'm troubleshooting a rifle for a family member. It's a DPMS AR-15 and it's not working properly after some rapid fire sessions he had with his son. The rifle will pick up a cartridge from the magazine (via charging handle and release lever) but often won't grab the next cartridge after successfully ejecting the spent casing. I see a slight marring on the casing that is ejected, not sure what information can come from that, but I've attached it. Today while testing I noticed when it didn't pickup the next round the forward assist could be used to move the BCG up another 1/8th inch. But still didn't fire as it didn't grab another round from the cartridge. I also noticed it not locking back on the last round.

So, here's what I've tried - I cleaned and oiled the buffer tube spring, ensuring it was properly torqued back down. I cleaned and lubricated the BCG at a field strip level. I tightened the magazine release by one turn. I've tried 6 different magazines from 4 different manufacturers. Including known working new PMAGs I use in my other rifles.

What else can I try before bringing it to a gunsmith?

Any help would be sincerely appreciated, I'm a noob with ARs.

shrxfn · Jan 3, 2017

Not a guru but I would try it with a known working lower to eliminate the lower, spring and buffer as the issue.

Whitebread · Jan 3, 2017

The bolt can't be going all the way back. It's not holding open. It's not loading. But when you rack it, it chambers a round. It's got to be short stroking. Fowling???

bsoileau24 · Jan 3, 2017

Dpms and other cheaper rifle are over gassed. I would try a heavier buffer to slow down the carrier speed. I would try at least a H buffer but I am sure a H2 would work also.

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southerner985 · Jan 3, 2017

did you try putting another BCG in the problem rifle to see if it feeds?

Sig220 · Jan 3, 2017

I would hazard a guess that you are under gassed....or too strong recoil spring. Sometimes, the gas block does not match the hole in the barrel, sometimes the hole in the barrel is not the correct size.

Information on the barrel length, stock type and home or factory build would help.

Basically, the bolt/carrier are not moving rearward enough to grab the next cartridge in the magazine when fired. Obviously it does when using the charging handle and the bolt release.

What do you torque when you say "I cleaned and oiled the buffer tube spring, ensuring it was properly torqued back down"?

I would spray the hell out of the bolt/carrier with Remington gun oil and try running it wet...sometimes a burr is smoothed out.....

bsoileau24 · Jan 3, 2017

Some dpms rifle use an aluminum gas block and I always wondered if it would expand differently enough from the barrel that it could cause a seal loss at that point.

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homeslice · Jan 3, 2017

Thanks for all for the prompt and helpful replies, I'll try to comment below my responses.

shrxfn - I don't have an assembled known working lower at this time, unfortunately.

Whitebread - where should I be looking for the fowling at?

bsoileau24 - Thanks, I'll hold onto that as an option once I move onto spending money on this thing.

southerner985 - I don't have another BCG at this moment. I do know a guy by proxy that builds a lot though that may have one

Sig220 - It's a carbine length rifle, factory DPMS I think, with a DPMS 6 position stock - traded from a member on here a few years ago and unfortunately that member has since passed away. Regarding the castle nut, etc, when I got it from my family member the stock was loose and moving slightly when turned.

If it's helpful I can snap some pictures - just need to know what to get detail pictures of. Thanks again everyone.

SpeedRacer · Jan 3, 2017

Sounds like it's short stroking. If it used to work, and now it doesn't, I'd wager it's a gas leak. Check the key on the carrier as well as the gas block. Make sure everything is tight and properly aligned, and look for carbon residue indicating a leak. Swap with known good components (different BCG, different upper) if possible to help identify the issue.

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rabiddawg · Jan 3, 2017

I agree it's undergassed. Look for leakage around the gas block, gas tube etc. look at the bevel on the tube where it mates with the gas key. You are looking for a nice consistent mating circle. If not your tube is out of alignment.

Make sure the gas key is tight.

homeslice · Jan 3, 2017

Gas key doesn't have any movement that I can tell. I took some pictures, can you see anything wrong? Looks like it also needs a more details cleaning around the locking lugs.

SpeedRacer · Jan 3, 2017

Maybe it's just photo distortion, but the portion of the gas key that accepts the gas tube looks bent in both pics, as does the gas tube. Or am I just seeing things?

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homeslice · Jan 3, 2017

SpeedRacer said:
Maybe it's just photo distortion, but the portion of the gas key that accepts the gas tube looks bent in both pics, as does the gas tube. Or am I just seeing things?

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Going check

homeslice · Jan 3, 2017

homeslice said:
Going check

Seems fine, must be the way the camera stabilizes or something (see it too in the pics), because it's not bent in relation to the two screws.

shrxfn · Jan 4, 2017

Probably not related to the issue but there seems to be a lot of green/yellow gunk on the bolt and in/around the chamber.

You can also check the gas port by removing the gas block and making sure if there is any carbon on the barrel it is centered around the gas port. Maybe the block came loose and the port is no longer centered to the hole in the gas block.

dougstump · Jan 4, 2017

Does the recoil feel soft & mushy, or does it have a sharp kick? If it's mushy, it's probably short stroking.

If it's a sharp violent kick, it may be bolt bounce. If the buffer spring is wore out or the buffer is too light, the bolt & buffer can smack into the back of the receiver extension and bounce forward before the magazine spring can push the next round up. I've run into this on a few rifles.

Also, if the magazine spring is shot you can get the same symptom.

homeslice · Jan 4, 2017

Went out to test the firearm to try running the BCG wet. Seems this didn't make the problem any better. I ran 3 magazines with 1 round each, none of which locked back. One FTE. I also noticed this fowling on the gas tube right behind the gas block, is this the leak?

Thanks again for all the help guys. The recoil doesn't seem abnormal to answer you, dougstump.

tallwalker · Jan 4, 2017

My impression is that it looks more like a rub than buildup but could just be the picture. Sounds crazy but is it possible that the tube is loose at the gas block like the pin is missing or something?

homeslice · Jan 4, 2017

tallwalker said:
My impression is that it looks more like a rub than buildup but could just be the picture. Sounds crazy but is it possible that the tube is loose at the gas block like the pin is missing or something?

I did try to scratch at it with my finger to see if it's carbon buildup, and it did seem to be. My guess would be after getting the gas block too hot during rapid fire it caused it to come loose? Is this something I can fix myself?

Sig220 · Jan 4, 2017

The carbon on the tube at the gas block would indicate a leak to me....which leads to not enough gas...which leads to the bolt/carrier not moving rearward enough to pick up your next round. If you have the tools, remove the handguard and check the gas tube/block make sure it has a pin in it holding the tube to the block. If not loose there, I would bet the block is not sitting over the hole completely.

DPMS AR15 Ejecting but not picking up next round

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