AR15 Help

[NWShooter44]

So I bought an AR15 from a buddy. its a stock DPMS lower with an A2 fixed stock, with a Bushmaster M4 upper.

First thing I did was to add all the usual magpul furniture. Went and got a collapsible magpul stock, and buffer tube kit (milspec)to convert from fixed to collapsible.

I took the rifle out a couple times to shoot, but every time it would either fail to eject, fail to chamber the next round or the bolt would lock back. So I took it down to Curts and had them go through the upper assembly and check out the gas system, and to remove/swap the triangle sight for a railed gas block. I was hoping that the gas system was to blame for my problems.

So I got my upper back and took it out last weekend to test out again, and every time it would fail to eject the round, and from what my buddy could see he thought it looked like the bolt wasn't cycling all the way back.

So my question is, what problem could I still be having???
Is there something different in a commercial spec vs mil spec buffer tube setup that could be causing this or do I have some other problem that I'm not aware of.

Thanks!!!

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[rick benjamin]

Bought from a buddy.
Replaced A2 fixed stock with collapsible stock and buffer tube kit.
Shooting reveals function issues
fails to eject
fails to chamber
bolt locks back unexpectedly.

Curtis replaced gas tube.
Still fails to eject.

Suggestion
The new buffer spring may be too strong.
Remove the collapsible stock and kit
Install the original A2 stock assembly.
Test fire for function

Suggestion
Since the gas tube was replaced,
ask Curtis if they cleaned the gas port in the barrel.

Suggestion
Dis-assemble the bolt carrier group.
Bolt carrier gas port clean?
Use Lighter fluid (naptha) and pipe cleaners.
The Bolt:
Observe the position of the three gas split rings, If the openings are close to being lined-up, the gas will pass without pushing the bolt enough.
The ring openings should be evenly staggered 1/3rd of the way around the circumfirence of the bolt.
(Like a clock face as an example, one should be at 12, one at 4, one at 8)
Lubricate bolt and bolt carrier, assemble. (ref operators manual) http://archive.org/download/milmanu...5-249-10_-_operators_manual_for_m16_m16a1.pdf
Test fire and report back.

 

[NWShooter44]

They also put a new gas block on and new gas rings

 

[308]

So I bought an AR15 from a buddy

Ask your buddy if he had any problems B4 selling to you. If he is honest, and it worked fine for him, then you can go from there and evaluate what is different between him shooting and you shooting.
Crappy low powered ammo will jam up an AR for sure...I know I love those double-feed pig piles in the chamber

 

[madcratebuilder]

They also put a new gas block on and new gas rings

Is the gas port and FSB ports aligned? That's the first thing I would check.

Don't worry about the gas ring alignment, as long as they are on the bolt they work. Needs to be well lubed.

What ammo, what mags?

 

[308]

Is the gas port and FSB ports aligned?

That's what I was thinking too. I've had one off a bit and while it ejected, it only tossed the spent case a couple feet away.

 

[osprey]

Ask your buddy if he had any problems. The chances that the gas system was at fault before the over haul and after is not likely. Did you use the same spring and buffer when you switched stocks. What ammo were you using? Inquiring minds want to know. The first thing I would try is a different mag. It could be that simple. If that doesn't solve the problem, I suspect the buffer is to heavy or the contact between the bolt and the hammer is incorrect .

 

[wichaka]

Check the above along with the gas key...make sure the two bolts are torqued tight.

If the gun is built correctly, aligning the gas rings will have no effect on function.

 

[speeddemon94]

Check the above along with the gas key...make sure the two bolts are torqued tight.

If the gun is built correctly, aligning the gas rings will have no effect on function.

To add to that, maybe the gas key was staked in a sloppy manner and it's catching in the upper.

But I would say the buffer spring is also an issue. We had soldiers that thought they could go get a collapsible stock and replace the A2 stock on their M16, and then couldn't understand why there was a problem...Did you use the same spring? The A2 spring is longer and meant to be used with a 20 inch barrel. There's my .02

 

[Taurus 617 CCW]

This problem can have a number of different causes. First and foremost I would try different ammo and magazines. Next, is there enough lube on the carrier and upper receiver?

One which you are already looking at is the gas system. There are many places where gas can leak from. Another problem that can cause short cycling is friction. Pull the charging handle back slowly and see if it feels smooth or if it feels like the bolt is dragging. Let me know if this helps.

 

[NWShooter44]

I'll look into this stuff tonight and report back. Thanks all

 

[Nwcid]

Did you change the buffer and spring when putting on the new stock? Fixed stock and collapsible use different ones.

 

[NWShooter44]

Yea I got a new spring, buffer, and buffer tube all from another forum member.

 

[NWShooter44]

Is the gas port and FSB ports aligned? That's the first thing I would check.

Don't worry about the gas ring alignment, as long as they are on the bolt they work. Needs to be well lubed.

What ammo, what mags?

Not sure what ports your talking about (FSB?) Still new to the AR world

 

[NWShooter44]

I've ruled out ammo because ive used an assortment of low and high quality stuff in it and the problem is consistent between all the rounds.

Used steel mags, and poly mags (PMAG and another off brand) and problem persists

Checked the gas key and it is tight.

Gas rings are aligned properly

Buffer spring used is a DPMS BS10A
Buffer tube is a DSA 6 position mil spec tube

 

[osprey]

When it does eject but fails to chamber a round is it resetting the hammer. I still suspect the bolt is maybe bearing on the hammer incorrectly and causing too much drag. Maybe try installing a different fire control group. Also it is possible the gas port in the barrel is too small or has material blocking it . Keep at it and you will solve it. It is part of the fun of an AR tinkering with them and getting them to run.

 

[eldbillbo]

did you all ready try everything rick benjamin suggested? thats the first thing to do

if those suggestions did not work , i can't see the factory gas block and the replacement that curt installed both being faulty

if all the above suggestions did not work then you have to consider a out spec part. gas port too small or in the wrong place. Misaligned locking lugs. out of spec gas key . out of spec extractor (btw how hard is the bolt cycle in and out by hand little resistance like you can shake it and it falls out or tip it and it falls out or you have to pull it out by hand and can feel the resistance )

have you already determined if it has the wrong or right buffer spring used.

where do you go shoot?

 

[rick benjamin]

At this point, I would re-install the A2 stock w it's buffer, spring, etc.
Shoot it. If it still fails,
Declare an emergency meeting at Applebys
We have your back

 

[NWShooter44]

its got the correct buffer spring. Checked that.
I think what osprey mentioned might be happening. Here's pics of the bottom of the bolt carrier and the trigger assy. It looks like its dragging a good bit.

I go up around squaw in estecada usually to shoot.

 

[wichaka]

The hammer will drag on the under side of the carrier, that's normal.

Go down Rick's list.