ar15 partial bolt close problem

[jontheturboguy]

Brand new dpms ar15.

Bolt will catch new round, then stop half way.

Foward assist won't engage.

Fully clean. Light oil, no oil, heavy oil.

New p mag, used gi mag and every flavor of ammo in between.

When bolt hangs open, you can engage charging handle, give it a light tug and the bolt will snap closed.

Held bolt stop closed manually with finger with same result.

Help?

 

[Tombs]

Please don't take the "did you make sure it's plugged in?" comment as an insult...

But are you sure you aren't riding the charging handle when charging the weapon?

 

[jontheturboguy]

Please don't take the "did you make sure it's plugged in?" comment as an insult...

But are you sure you aren't riding the charging handle when charging the weapon?

Yes....

The partial bolt hang open does it when weapon us cycled by firing the first round.

 

[DanVoils]

Almost sounds like a gas tube alignment problem.
Try pulling the bolt out of the BCG and see if it will cycle in properly. This takes the bolt/cartridge feed out of the equation. If it still hangs then look at the leading edge of the gas key on top of the BCG and see if there's any indication of it hitting the tube. (Take a sharpie and color the leading edge of the gas key. This will help in seeing if there's any interference.)
If it goes fine then make sure the bolt itself isn't binding up.
Hopefully you are testing this with Snap Caps or some sort of dummy round. If the firing pin is hanging forward you can get a slam fire.

 

[Leo]

"Almost sounds like a gas tube alignment problem."

I think Dan called it right. That would be my guess, there is just not that much that can hang things up.

Good Luck

 

[jontheturboguy]

I think I'm not stating my problem correctly:
-Cycle the weapon manually it cycles fine
-Cycle the weapon by firing the first round and the bolt & bolt carrier will eject the spent cartridge, strip the new round from the magazine, and fail to go into full battery by a 1/2" or so.

 

[Jarhead1775]

Is this rifle a Carbine model or a A1/A2 variant?

The buffer spring would be a good one to look at IMO. I have seen a Carbine length spring installed in a fixed stock variant and cause a similar issue while I was an Armorer.... That one took a lot of head scratching and to figure out.

Another place to look would be the buffer. Too light and it will not cycle properly or if the weights are stuck in the buffer it will not transfer all the momentum. Shake it and see if it rattles.

If you have another to borrow a spring and a buffer from or a buddy that will loan them to you... that is where I would start after the obvious obstruction inspections and a functions test.

Yes, they all seem to be dumb problems, but most situations are dumb to begin with.

 

[DanVoils]

I think I'm not stating my problem correctly:
-Cycle the weapon manually it cycles fine
-Cycle the weapon by firing the first round and the bolt & bolt carrier will eject the spent cartridge, strip the new round from the magazine, and fail to go into full battery by a 1/2" or so.

Got it. I thought it wouldn't manually cycle.

Is this rifle a Carbine model or a A1/A2 variant?

The buffer spring would be a good one to look at IMO. I have seen a Carbine length spring installed in a fixed stock variant and cause a similar issue while I was an Armorer.... That one took a lot of head scratching and to figure out.

Another place to look would be the buffer. Too light and it will not cycle properly or if the weights are stuck in the buffer it will not transfer all the momentum. Shake it and see if it rattles.

If you have another to borrow a spring and a buffer from or a buddy that will loan them to you... that is where I would start after the obvious obstruction inspections and a functions test.

Yes, they all seem to be dumb problems, but most situations are dumb to begin with.

I agree. It sounds like the buffer system isn't acting properly. I suggest doing what Jarhead1775 said and see if that will resolve it.

 

[mvician]

Sounds like the bolt carrier hanging on the hammer

or

when the round is feeding it is getting hung up going into the chamber

factory DPMS or home build ?

 

[Jarhead1775]

Being open only 1/2" the hammer has been reset. The last 1/2"ish is the bolt camming into the chamber...unless there is 1/2" of brass exposed.... then that is a different story altogether and you might be onto something.


Upon rereading the first statement he states a slight tug on the charging handle and it snaps shut, yet the FA will not engage.

Does the FA not move or not do anything? Not moving is an issue, not doing anything is a blockage/jam issue.

Hell... I might even check to see if the barrel nut is tight... human error is more common then ever. If it were to be loose... the barrel "could" be slightly off cant and cause the bolt to impact the chamber lugs. The slight tug... helps to realign the bolt and chamber lugs.

 

[g3man]

Do you have another upper/lower to see if the same symptoms can be recreated thus narrowing down if it is in fact an upper or lower issue?

 

[XDLover]

Is the round seating? It almost sounds like the brass may not be in.

 

[jontheturboguy]

I have narrowed it down to a faulty / poorly machined bolt carrier. I have exchanged EVERYTHING including lower and upper and all associated parts. The bolt carrier however I can recreate the problem almost every time.

 

[Jarhead1775]

That sucks, but I'm glad you got it narrowed down. Most of the AR platforms are either go or no-go... apparently you got one of the few no-go f ups.

Hopefully DPMS will honor the Manufacturers defect warranty and make it right.

If not, there are many superior BCG's on the market. LMT makes an awesome Enhanced BC, Bolt or entire BCG. They make them in both semi-auto and full-auto varieties. I'm biased because this is what I run in my LMT...

Good luck and keep us updated

 

[jontheturboguy]

Dpms.....as it turns out, only mfg my lower - not the complete rifle.

AR15 V. M16 Bolt Carrier - M4Carbine.net Forums

I have the sp1 bolt carrier and the hammer catches on the firing pin causing the hang up.

Installed the m16 style carrier and WALA problem went away.

Now I need a 16 style carrier.

 

[netsecurity]

Check palmettostatearmory.com.

 

[mvician]

Sounds like the bolt carrier hanging on the hammer


factory DPMS or home build ?

Dpms.....as it turns out, only mfg my lower - not the complete rifle.



I have the sp1 bolt carrier and the hammer catches on the firing pin causing the hang up.

Installed the m16 style carrier and WALA problem went away.

Cool........glad you got it

 

[jontheturboguy]

Can any one shed some light on why my bcg would be machined like this?

 

[mvician]

Bolt Carrier/Hammer issues - AR15.COM

SP1 Carrier hang up problem *Resolution at bottom of thread!* - AR15.Com Archive

How to tell if I have small spool AR-15 firing pin or a large spool M-16 firing pin? - AR15.Com Archive

 

[mvician]

Can any one shed some light on why my bcg would be machined like this?

Unprotected firing pin and notched hammer - AR15 Armory.com