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-   -   Someone please help. Problem with my target AR (http://www.firearmstalk.com/forums/f20/someone-please-help-problem-my-target-ar-79794/)

DarinCraft 12-30-2012 03:53 AM

Someone please help. Problem with my target AR
 
My target AR constantly short cycles.

1. Numerous times when shooting I will have an empty chamber and will have to cycle it manually. It appears the bolt is not cycling back far enough to pick up the next round in the mag.

2. Every time the last round is fired the bolt will hold open on the follower and not on the BHO. I have to manually pull the bolt back another 1/2" before the bolt will catch on the BHO.

3. It will ALWAYS eject the spent case and never stovepipes.

4. If I have to extract an unspent round for some reason, it take a TON of effort to pull the bolt from battery as if the chamber is too tight.

SPECS-
Pre built DPMS upper with a 16" SS bull barrel.

I have put two gas blocks on it, cleaned the gas tube and gas port.

CMMG lower with DPMS LPK

Carbine buffer and spring.

I have swapped this upper on my other AR with no change in performance. I am starting to think either the headspace is too tight or there is something wrong with the gas system.

Please help.
Darin

Jpyle 12-30-2012 04:29 AM

1. Did the problem appear gradually with infrequent short cycles increasing to the current situation or did it appear suddenly?

2. Is the gas block seated properly? Any visible signs of gas escaping under the port?

3. Do you shoot a lot of steel cased ammo? Are the rims being torn off the cases?

4. What type and weight buffer? H1, H2, etc

Difficult to diagnose over the internet but given the problem can be repeated on a different lower points to the upper. Quite possibly the gas block port is not 100% in line with the barrel port. It happens, many folks simply line the gas block up with the shoulder cut in the barrel and pin it down...sometimes a little finesse is required. Goes without saying, make sure the gas key is securely attached to the carrier and there is no "mushrooming" of the tube end.

For the sticky extraction, try a chamber brush and some Hoppes. Steel ammo, if you shoot it, can leave a residue in the chamber that can gum up when reheated and adhere the brass to the chamber walls.

willfully armed 12-30-2012 04:56 AM

Are the gas key screws tight? Are the o rings lubed?

DarinCraft 12-30-2012 04:58 AM

Quote:

Originally Posted by Jpyle (Post 1071614)
1. Did the problem appear gradually with infrequent short cycles increasing to the current situation or did it appear suddenly

Has been a problem since the first day of operation.

Quote:

2. Is the gas block seated properly? Any visible signs of gas escaping under the port?
There are signs of gas escaping back toward the receiver, however happened with both gas blocks. There is a relief dome inside the gas block that allows a shadow of carbon to be left behind on the barrel. The gas port on the bbl is dead center of that shadow.

Quote:

3. Do you shoot a lot of steel cased ammo? Are the rims being torn off the cases?
I shot steel for a couple of hundred rounds, but switched out. The rims were not torn off. I would have to use a rod to get the case out.

Quote:

4. What type and weight buffer? H1, H2, etc
Standard M4 civilian buffer and spring that comes with the cheapo collapsible stocks.

Quote:

Difficult to diagnose over the internet but given the problem can be repeated on a different lower points to the upper. Quite possibly the gas block port is not 100% in line with the barrel port. It happens, many folks simply line the gas block up with the shoulder cut in the barrel and pin it down...sometimes a little finesse is required. Goes without saying, make sure the gas key is securely attached to the carrier and there is no "mushrooming" of the tube end.

For the sticky extraction, try a chamber brush and some Hoppes. Steel ammo, if you shoot it, can leave a residue in the chamber that can gum up when reheated and adhere the brass to the chamber walls.
I'll try that. Thanks for the help JPYLE, I really appreciate it

DarinCraft 12-30-2012 05:18 AM

Quote:

Originally Posted by willfully armed (Post 1071642)
Are the gas key screws tight? Are the o rings lubed?

The screws are tight, but what O rings?

willfully armed 12-30-2012 05:30 AM

The o rings on the bolt, inside the carrier.

Clean your chamber as well. Brakleen does exceptionally well on removing chamber deposits.

DarinCraft 12-30-2012 05:33 AM

Quote:

Originally Posted by willfully armed (Post 1071668)
The o rings on the bolt, inside the carrier.

Clean your chamber as well. Brakleen does exceptionally well on removing chamber deposits.


Wow well I feel stupid because I had no idea there were o rings there. I'll check tomorrow and post up. Thanks WA

Quentin 12-30-2012 06:02 AM

Don't go looking for rubber O-rings though, just three steel gas rings on the bolt.

Jpyle 12-30-2012 06:05 AM

Quote:

Originally Posted by Quentin (Post 1071684)
Don't go looking for rubber O-rings though, just three steel gas rings on the bolt.

http://4.bp.blogspot.com/-7PYAenQhoZ...s1600/Bolt.jpg

Txhillbilly 01-01-2013 12:04 AM

I'd say you have a buffer spring problem. I had the same issue with my DPMS LR-260,it was jamming,short cycling,and the bolt wouldn't stay open after last shot.
I could manually pull back the bolt,and it would lock open,but firing the rifle it wouldn't.
I ended up cutting 3 coils off the buffer spring,and all issues disappeared. The rifle works like a champ now.


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