AR trouble shooting - repair suggestions

[greg1996zz]

I have a DPMS 5.56 carbine that has been 100% reliable for many years. A couple of days ago I fired about 30 rounds and then it stopped extracting shells and the cases were stuck in the chamber. I had bang the butt on the bench while pulling the charging handle to get the cases out. Did this about 20 more times before going home.

I hoped the problem was simply the old 1983 Malaysian suplus ammo that I using. I inspected the gun, gave it a thorough cleaning and went back to the range today using Winchester ammo. Same problem, except I could, with some difficulty, extract the spent cases with just pulling the charging handle. I shot a couple of rounds while just looking at the bolt and it does not move at all. i.e. it's not short stroking. It's like the gas has just suddenly been turned off. The gun went from perfect to non-functional in one shot.

So, here's what I've inspected:

• gas block is secure and gas tube pin is in place
• no visible damage to gas tube.
• gas key secure and free of obstruction
• no visible damage to bolt or lugs - gas rings look fine.
• no visible issues with the carrier
• chrome lined chamber/bore are clean - no scratches, rust, pits, etc.

Before the problem started I changed the standard A2 buttstock for a Magpul fixed stock, but I did not have to mess with the buffer tube or buffer to do this.... it's just one screw to make the swap. Nonetheless, I pulled out the buffer spring and buffer and they look fine.

Suggestions? What else can I check? Stuff breaks, i can live with that, but not knowing what the problem is drives me nuts.

Alternatively, who would you take the gun to in the OKC area to fix it?

I'm pretty handy, but I'm not going to plays where's Waldo and randomly replace one item at a time hoping to figure it out.

Thanks.

 

[NightShade]

First thing I would do is check the gas block and tube for an obstruction. If you had to mortar the rifle to extract the surplus ammo the stuff may have been out of spec IMHO and who knows what it could have done down the bore. You could also just put a round in the chamber and extract it by pulling the charging hammer to see if something is acting up there as it should extract easily.

I would probably pull the gas bock and tube and look at the gas hole in the barrel and the gas tube/gas block as even if you can get some flow through it some crud inside of it will cause issues. I hose mine down with CLP every few hundred rounds to keep it clear. Basically I open up the chamber and spray it down through the tube when I am at the end of my session and let it sit a few minutes then pump a couple rounds through and let the gas blow the crud out and then hose the bcg down.

 

[Jedabug92]

I may have missed it, but did you check the extractor?

Sent via carrier pigeon

 

[lasher]

look at the bolt lugs, and at the extension lugs. maybe some brass flakes stuck in there which would reduce your headspace and the bolt is so tight it won't turn and move? had a similar problem with a brand new bolt, it was enough out of spec that it locked totally up in battery and could not be moved. vendor sent a new bolt and problem was solved, but i have also had brass flakes/shavings give me grief as well

 

[mr ed]

While chrome lined chambers are made to resist rust. they don't always.
1. I would spray down the chamber / locking lug area with an evaporating cleaner. carb/brake cleaner.
and inspect with light.
Barrel made be chromed but lug area usually isn't and can crud up good.
2. Lubricant is your friend. I like mine juicy.

 

[greg1996zz]

I may be zeroing in on the problem. I sorta took nighshade's suggestion. I stood the upper up and shot several drops of CLP down the gas tube. It ran down the gas tube into the barrel and left a nice little puddle on the paper. Next, I disassembled the bolt carrier group and filled the gas key with CLP and it doesn't flow. It's been sitting vertically with gas key full of CLP for 10 minutes and it's still full. It should flow right through into the interior of the carrier, right?

 

[lasher]

yep, should run thru, try a pipe cleaner, i usually run a pipe cleaner thru them to get excess CLP out after a good cleaning

 

[zghorner]

agree with the above, if the BCG isn't moving at all i would think gas issue. Not sure what kind of gas block you have but could it be that the gun was dropped causing the gas block to rotate out of alignment? If an A2 FSB with pins i doubt it could happen but just a thought.

 

[Ignored Member]

You shouldn't have any obstructions in the gas tube. Cleaning a gas tube after running ammo that puts thousands of psi of pressure running through it will certainly clean any obstructions you may have.
My best guess would be that there is either a misalignment somewhere, or there's a hole/crack in the gas tube or an excessive gap in the gas block.

 

[greg1996zz]

There was a freaking primer lodged in the gas key!!! I was able to carefully drill out the middle of the primer, get a long screw into it and pull it out.

Who could have ever guessed that one? I appreciate you guys helping me brainstorm the problem.

ETA - in the original post I said the gas key was free of obstruction. The primer was lodged perfectly square in there so that it looked like I was looking at the bottom of the gas key.

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