Bolt won't lock on last round, input and suggestions!

[straitR]

FYI- I was recently contacted after someone else had a DD issue. Turns out the gas port was undersized and that's why it wouldn't run. The stand off of your gas block from the shoulders seems odd, but the block is pinned so it couldn't have moved. I do agree it looks like the roll for the gas tune is missing.

I think he confirmed the GB roll pin is still there (post #11), just a deceptive picture.

General comments...

If the gun ran fine for 1000 rounds, then begins to short stroke, print keyholes, and has a POI shift at that round count then it's something more uncommon than what causes typical under gassed issues on a fresh build.

Ammo - All of those things point to crap ammo, but he's using XM193. Benefit of the doubt, I guess.

Bore - Mostly for the keyhole/POI shift, but OOS bore can exacerbate short-stroking if the gas port is undersized to begin with. More common with steel cased, but again, XM193 being used. It hasn't been mentioned, but has the OP inspected the bore? It's a known quality barrel, so I doubt he's having bore issues at 1000 rounds, but why not look?

And the most uncommon thing I've ever seen progressively cause those three things, copper fouling built up in the gas port, created by a notably large burr on the muzzle side of the gas port that was big enough to not be shot out. Have you noticed excessive copper fouling on the bolt in the past?

[npena84]

Yeah the pin is still in there. I must be some kind of photographer. I took the pic form about the only angle, that you can see straight thru the hole. StraitR, what should I be looking for in the bore? I haven't noticed any copper fouling out of the ordinary.

[npena84]

Here are some more pics of the bolt carrier, if it helps. They tube on my carrier key looks slightly bent. Idk if that is an issue or not. But overall does that look like a carrier should after 1000 rounds?

[SteveL]

Here are some more pics of the bolt carrier, if it helps. They tube on my carrier key looks slightly bent. Idk if that is an issue or not. But overall does that look like a carrier should after 1000 rounds?

The flat area of the gas key around 10-11 o'clock could possibly be problematic. Has it ever been dropped?

Disassemble the BCG and then take just the carrier and slide it into the upper very slowly. See if you can feel it rubbing or binding when the gas key meets the gas tube.

[straitR]

Yeah the pin is still in there. I must be some kind of photographer. I took the pic form about the only angle, that you can see straight thru the hole. StraitR, what should I be looking for in the bore? I haven't noticed any copper fouling out of the ordinary.

I suggest that you thoroughly clean your bore/barrel then inspect from both ends and look for obvious impediments or damage (throat erosion often looks like chips). While a bore issue is highly unlikely, given the manufacturer and round count, anything is possible. There's clearly something out of the ordinary about your problem, because the three issues you're having do not typically occur together on a low round count rifle shooting known good ammo.

Take care to note the condition of the gas port hole, and bore/throat. Pics of recently fired brass could be extremely helpful as well, if you have any.

[556BlackRifle]

The flat area of the gas key around 10-11 o'clock could possibly be problematic. Has it ever been dropped?

Disassemble the BCG and then take just the carrier and slide it into the upper very slowly. See if you can feel it rubbing or binding when the gas key meets the gas tube.

Good eye Steve. I missed that. What do you think about the wear pattern on the 12 O'clock lug?

[SteveL]

Good eye Steve. I missed that. What do you think about the wear pattern on the 12 O'clock lug?

Hard to say really. I'm just trying to figure out what has changed in this rifle to suddenly cause it to start having these issues. Given that the gas key should not have a flat spot on it I would suggest starting there.

[BufordTJustice]

Hard to say really. I'm just trying to figure out what has changed in this rifle to suddenly cause it to start having these issues. Given that the gas key should not have a flat spot on it I would suggest starting there.

The recent key holing is a huge red flag for me.

[npena84]

So DD got back to me today. I'm gonna be sending out the upper to them tomorrow morning. They said they think the issue maybe the bolt carrier. Who knows, I'm sure they will figure it out. I will keep everyone posted on the issue. Because I would really love to know what is going on. And maybe find out what happened in the first place. You guys really have been a great help. And I appreciate and am humbled by all your responses.

[Marler5811]

Caroline will make sure you're taken care of. For this type of malfunction, we'll definitely focus on the gas system for starters. This is a classic symptom of short stroking which makes me think there is a gas leak somewhere or not enough is being funneled through the port in the barrel. Our armorers will go through it with a fine toothed comb and repair/replace anything that's found out of whack.

The key-holing very odd for a barrel with such a low round count. do you have a photo of the target that you can email to me?