Help Pls: WHAT In the world is THIS??

[RET15]

Asking for some of your expert opinions on an AR issue. I’ve done a few AR builds a and my most recent a 300blk. I put about 500 rounds (supersonic) through it without a single issue. I then added a Q Full Nelson suppressor and moved to subsonic. I put about 25 rounds through it to test with no issue. Yesterday, I go hunting for the first time and my bolt locks up like a drum. Wont budge. Have to mortar method the live round out to free the bolt. Do it again, keeps jamming. Open it up and find a small amount of debris in and around the chamber and in the barrel so I clean them both super thorough and retry—everything works fine. Put ONE subsonic suppressed round through it to test fire before hunting and it works fine. Go hunting, pull the charging handle in the blind at 5am, locks again. Go through the same procedures and get it home. Open it up and I find THIS. See pictures. I cleaned this upper, bolt and barrel to a mirror finish with absolutely NO particles or residue last night. This is from ONE round and it’s a mess. ONE. It almost looks like brass shavings as they are very fine particles but abrasive. But how could this happen only after one round? My barrel also has significant black debris in it also after the one round.

I’ve heard that suppressors can cause a backflow of gasses that can cause debris after a while, but I assume the debris would be black and take a while to accumulate.

I’m hoping someone with Suppressed AR experience can help me figure this out and maybe offer a solution? One round bolt lockups aren’t gonna work for me. Could this be a suppressor issue? If not, has anyone seen this before?

As always, your input is truly appreciated.

RF

 

[edwardware]

That's the underside of an AR upper receiver, facing forward into the barrel extension, showing the M4 feed cuts. Looks good.

Oh, you mean the powder residue? That's powder residue. Pretty yellow isn't it?

Every round makes it, and low-pressure rounds, especially with powder that's not well-suited to low pressure, make a lot more of it. Your powder isn't combusting completely. If you're handloading, you need to change powder or increase charge.

Brush most of it out with a toothbrush, re-grease, rock on.

 

[RET15]

That's the underside of an AR upper receiver, facing forward into the barrel extension, showing the M4 feed cuts. Looks good.

Oh, you mean the powder residue? That's powder residue. Pretty yellow isn't it?

Every round makes it, and low-pressure rounds, especially with powder that's not well-suited to low pressure, make a lot more of it. Your powder isn't combusting completely. If you're handloading, you need to change powder or increase charge.

Brush most of it out with a toothbrush, re-grease, rock on.

So that much residue from one round? Enough to cause my bolt to lock up after firing one shot? These are the bullets I’m using. They’re from Discreet Ballistics. Supposedly designed for low pressure and high expansion suppressed. Got a million good reviews.

 

[edwardware]

So that much residue from one round?

Yes, a sufficiently low pressure round can turn most of the powder into yellow crud, and that's definitely powder residue. I'd be in contact with the manufacturer of that fancy-looking ammo. . .

 

[WestKentucky]

I had some trash 22 rounds doing that to me. Looked just the same in my guns. I agree with the others, it’s unburned or poorly burned powder residue.

 

[RET15]

Thank you both. I also just noticed that when the bolt was locked forward, it took 0.1325 inch off of the OAL of the bullet. This is a bad situation all the way around. After everyone’s much appreciated input, I’m thinking the root of all this is the stupid ammo. Just hoping it didn’t do any damage to the barrel or BCG.

 

[CapnMac]

Barrels and BCG are tough. You have to work hard to get a bulge or cracked lugs.

That round needs a different powder. It may be subsonic, but it is not suppressor-friendly.
As a guess, a pure-D guess, it needs a smaller charge of a hotter powder. Or, a much slower powder that will continue to burn even when vented down the gas tube and ported off into the suppressor.

 

[RET15]

Thanks Cap’n. I’m trying to reach the manufacturer to see what they used and show them what happened. Getting enough residue to lock the bolt forward after a single round is BS....lol

 

[Project355]

Long time ago now, I chanced to have an impromptu conversation with the late John Noveske about barrel port sizing. Suppressor needs smaller gas port maybe different buffer to keep things running right. Take off the can, you may be undergassed, use a Flaming Pig. The two barrels I got from him were ported for suppressor use, not open end use.

Just throwin' that out there for brain fodder.

 

[edwardware]

I also just noticed that when the bolt was locked forward, it took 0.1325 inch off of the OAL of the bullet.

OAL of the cartridge, not the bullet.

That is really, really not good; don't shoot that. It's very unlikely you harmed anything, but no need to continue pushing it.

 

[EccentricInTexas]

TULAMMO Leaves Yellow snow. I have seen it in their 380 Pistol ammo. The rounds look like they missed seated the bullets. That might effect the powder enough to cause the excess yellow snow.

 

[mjsdwash]

bad powder, and really underloaded powder does exactly that. Sticky chamber sounds like excessively long loads. I have seen that residue on Russian steel ammo, it clocked around 2600fps so clearly not a optimized load.
I have had that chambering issue with my 300AAC, slightly shorter seating fixed it.
A rifle has to be far, far dirtier than that to jam.
The AR is not any dirtier than any other design because of the gas tube. Most of the gas is directed into the charging handle, or the BCG, and the chamber is actually cleaner the soviet stuff because the chamber remains sealed until the case is almost fully extracted. If you have soot blowing into the locking lugs of an AR, your gas tube is ruptured. I only mentioned this because an AR actually runs fairly clean when loaded with correct pressures.

 

[243winxb]

https://www.hornady.com/support/superformance-in-gas-operated-firearms

the gun is still in the process or firing while it’s trying to extract the cartridge case.

With the installation of an adjustable gas system

Ammo looks like it needs a good crimp to keep the bullet from moving too soon? Or more neck tension/bullet hold?

 

[herrwalther]

I had the same residue in a short barreled handgun shooting Golden Saber 124+p 9mm. Same ammo works fine in my other 9mms. I switched ammo for that gun and hasn't happened since.

 

[jmorris]

Got a million good reviews.

And one bad one.

I put about 500 rounds (supersonic) through it without a single issue.

Makes the rifle sound OK.

I then added a Q Full Nelson suppressor and moved to subsonic. I put about 25 rounds through it to test with no issue.

Still makes the rifle sound Ok and the suppressor didn’t make it choke, at least after 25 rounds.

Yesterday, I go hunting for the first time and my bolt locks up like a drum. Wont budge.

Makes me wonder what took place between the 25 rounds that were tested without any issues and the lock up?

Same ammunition or did you change something, anything?

I’m thinking the root of all this is the stupid ammo.

If the first 25 rounds didn’t run flawlessly, I would agree; however, that doesn’t account for a rifle that ran perfectly, was put up and locks up with the next round chambered. Is subsequently cleaned and locks up again after a single round.

I do concur with the others, that’s powder residue not brass.

Suppressors make firearms get dirty quicker as do incorrectly chosen powders/charge weights. That’s a lot for a single shot.

*** Almost looks like a bullet got stuck in the bore then the case was extracted, dumping the entire charge inside the action. Was your set back round one that was subsequently attempted to be chambered? If so, I would look for a bullet stuck in the barrel.***

 

[BBBBill]

Many folks who run them with and without suppressors use an adjustable gas block.

 

[RET15]

Damn...stupid email isn't alerting me--didnt even know these were there--sorry. Not sure why no email, everything is set up correctly.

Thanks all for the responses. I did check to see if I had a squib, but nothing in there. The first 25 rounds were supersonic--the issue only started with the can--and this ammo. Really feeling like the ammo is the cause of it. I've been trying to find some other subsonic 300 blk to test, but you can imagine how that's going. I may fire a couple of supersonic through the can just to see.

 

[RET15]

BTW, it's a 16 inch barrel with pistol length gas.