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AR15 Upper Problem

armilitearmilite Member Posts: 35,160 ✭✭✭
edited December 2011 in Ask the Experts
Okay you think I'd be able to figure this out myself but this problem is getting more perplexing the more I think about it. I have a Colt Match Target lower receiver, no problem there. On top of this I have a DPMS left handed upper receiver with a DPMS left handed BCG.
When I shoot this the BCG goes haywire. It may eject, it may not sometimes it extracts but doesn't eject. Sometimes nothing happens and it acts like a bolt action. I'm pretty sure it isn't the gas block as I have moved it around thinking it may not be lined up with the gas port on the barrel. Now is there a fool proof way of aligning this. The barrel is a Lothar Walter 24" bull barrel with a .920 barrel diameter and it has the set screw hold down for the gas block.
I was thinking of just poop canning the DPMS upper and BCG and going with a Stag upper receiver and BCG. I picked the DPMS stuff up before Stag came out with their left handed stuff.

Now to complicate this more I was looking at Brownells web site to see if they carry any Stag parts and low and behold they do carry left handed uppers and BCG's.
While looking at their Stag line I noticed something that jumped out and hit me in the face.
They list a left handed barrel extension. I've never seen this before as they say this is machined so that the bolt can turn in from the left hand side as well as the right hand side.

Is this something I may have over looked??? I've never heard of a left handed barrel extension could this possibly be the reason why this rifle is acting so erratic??

Thanks in advance.

Comments

  • MobuckMobuck Member Posts: 11,434 ✭✭✭
    edited November -1
    I'm not really familiar with the left hand uppers but I don't think the bolt rotates opposite the righties. Just the extractor& ejector positions are reversed and for all I know, the bolt may just be rolled over 180*.
    It sounds like you have a gas problem. I've used a sharpie marker and caliper to determine the proper alignment of the gas block and apparently got it right since the rifle works 100%.
  • RidgeriderRidgerider Member Posts: 57 ✭✭
    edited November -1
    You dont need a left handed barrel extension. There is a company called Quality Arms Idaho who make a complete ambidextrous AR15 that will eject either to the right or left depending how you set it up. You have a gas problem either the ports are not lined up and to check it mark the position of the block to the barrel. Pull the gas block off and there should be a complete circular burn mark around the port in the barrel adjust accordingly if not concentric. The gas is not getting to the bolt you may have a loose gas key or a worn gas tube.
  • armilitearmilite Member Posts: 35,160 ✭✭✭
    edited November -1
    quote:Originally posted by Ridgerider
    You dont need a left handed barrel extension. There is a company called Quality Arms Idaho who make a complete ambidextrous AR15 that will eject either to the right or left depending how you set it up. You have a gas problem either the ports are not lined up and to check it mark the position of the block to the barrel. Pull the gas block off and there should be a complete circular burn mark around the port in the barrel adjust accordingly if not concentric. The gas is not getting to the bolt you may have a loose gas key or a worn gas tube.





    quote:AR-15 AMBIDEXTROUS BARREL EXTENSION
    Mfr:STAG ARMSStatus:In Stock


    M4-style Ambidextrous Barrel Extension has specially-chamfered lugs for use with the left-handed bolt assembly. Also works with standard, right-handed bolts. Gunsmith installation required.

    The above was taken from Brownells website but there was something else I read about it last night about a reverse bolt rotation and was cut slightly different.

    I also agree with the gas block, but I think it would mount right up against the barrel step which is where I had it originally. It didn't work there either. I moved it slightly forward and it did the same thing. All parts are new so nothing is worn out.
  • armilitearmilite Member Posts: 35,160 ✭✭✭
    edited November -1
    quote:Originally posted by Mobuck
    I'm not really familiar with the left hand uppers but I don't think the bolt rotates opposite the righties. Just the extractor& ejector positions are reversed and for all I know, the bolt may just be rolled over 180*.
    It sounds like you have a gas problem. I've used a sharpie marker and caliper to determine the proper alignment of the gas block and apparently got it right since the rifle works 100%.




    I've done 4 or 5 others as well and have never had a problem. Like I said above normally you mount it right up to the barrel step and everything usually works. In this case its not working.
  • RidgeriderRidgerider Member Posts: 57 ✭✭
    edited November -1
    M4-style Ambidextrous Barrel Extension has specially-chamfered lugs for use with the left-handed bolt assembly. Also works with standard, right-handed bolts. Tells me its not necessary.
    Remove gas tube. Remove set screw. Rotate gas block 180 degrees until set screw hole is over the gas port this will show if the gas block set back is correct.
  • armilitearmilite Member Posts: 35,160 ✭✭✭
    edited November -1
    quote:Originally posted by Ridgerider
    M4-style Ambidextrous Barrel Extension has specially-chamfered lugs for use with the left-handed bolt assembly. Also works with standard, right-handed bolts. Tells me its not necessary.
    Remove gas tube. Remove set screw. Rotate gas block 180 degrees until set screw hole is over the gas port this will show if the gas block set back is correct.



    I agree with you about the barrel extension as this just caught me off guard. I'll try what you recommended but this block has 3 set screws and I'm not sure if the set screw hole would line up with the hole in the gas port. Thanks



    Well I went and took everything apart and the third hole did line up with the port in the barrel. Had to go in and remove a bit of metal from around the barrel and in the gas block where the screws had caused some of the metal to almost fuse the two together. Now the gas block slides right on the barrel and everything is lined up where it should be. Now if it doesn't work the problem is definitely somewhere in the BCG group.
  • azpowerwagonazpowerwagon Member Posts: 376 ✭✭✭
    edited November -1
    May also double check the gas port hole in the barrel to make sure it is of the correct diameter and not obstructed.
  • armilitearmilite Member Posts: 35,160 ✭✭✭
    edited November -1
    quote:Originally posted by azpowerwagon
    May also double check the gas port hole in the barrel to make sure it is of the correct diameter and not obstructed.



    Everything is fine there and now everything is lined up as well. But it wasn't like it was off that much to begin with and I actually blew into the gas tube and it is lined up and clear as well.
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