Help!! AR 15 experts..

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Help!! AR 15 experts..

Post by staples on Mon May 02, 2011 8:40 pm

I'm in need of some professional opinions, I'm going crazy ha. I just put together an AR yesterday and thought everything was peachy. All parts are new, its a 20" barrel with rifle gas system using a rifle stock. I didnt get a chance to shoot it until this afternoon when I noticed it was short stroking. I used a known good magazine and just loaded one shell and it fires but the bolt will not hold open after cycling , I repeated this several times with the same results. Mag with more than 1 round will fire but not load another shell. I tried 3 different kinds of ammunition (wolf, remington, federal). The bolt moves far enough back to release the dust cover but not chamber another round. I swapped out the bcg with one I know that works and it still short strokes. I put the new upper on a carbine lower just out of curiosity and it still short strokes. I removed the gas tube and gas block (both are brand new) and verified the tube is installed correctly. I can blow air through it freely and feel it coming out the gas port. I am out of ideas why this thing is shortstroking???? What do you guys think? Thanks in advance!

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Re: Help!! AR 15 experts..

Post by bsdubois00 on Mon May 02, 2011 9:07 pm

What Buffer do you have? Also is it a rifle stock or a carbine adjustable stock?

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Re: Help!! AR 15 experts..

Post by staples on Mon May 02, 2011 9:17 pm

Its the standard rifle buffer with rifle spring in an Ace Skeleton rifle stock.

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Re: Help!! AR 15 experts..

Post by SubGunFan on Mon May 02, 2011 9:18 pm

Pull the bolt carrier and check the 2 allenhead screws that connect the gas port (aka: hood scoop). If those screws are loose, you are losing gas pressure to the bolt. Thus, the short stroking. Those 2 screws need to be staked after they are tightened.

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Re: Help!! AR 15 experts..

Post by staples on Mon May 02, 2011 9:30 pm

Thanks, I checked the screws, they are nice and tight. The bolt carrier is practically brand new with less than 200 rounds through it. I'm clueless what could be the problem

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Re: Help!! AR 15 experts..

Post by SubGunFan on Mon May 02, 2011 9:34 pm

Has your bolt carrier group and upper ever worked right....?

You state less than 200rds though it.........

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Re: Help!! AR 15 experts..

Post by SubGunFan on Mon May 02, 2011 9:37 pm

Look at all the locking lugs around the bolt. Do you see any shiney (bare metal) spots on the lugs? This could mean your bolt and barrel extention are not mating up correctly.

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Re: Help!! AR 15 experts..

Post by staples on Mon May 02, 2011 9:50 pm

The bcg was from another rifle that had hardly been shot, it worked fine in that rifle( 200 rounds). The upper that the bcg group is in now is all brand new parts and it has been short stroking from the get go. I even put in another bcg from a different rifle with the same results. I checked the lugs and the bottom 3 do show a little shiney, im guessing this is not good?? Also I noticed if I blow really hard in the gas tube I can hear the very faintest hiss from the gas block. Could the gas block be leaking as well? Thanks again for the help!

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Re: Help!! AR 15 experts..

Post by SubGunFan on Mon May 02, 2011 10:24 pm

Sounds like your new upper is out of specs. Maybe the barrel is not screwed in correctly. This will take special tools and know how........

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Re: Help!! AR 15 experts..

Post by staples on Mon May 02, 2011 10:38 pm

That doesnt sound too good, I better get it to the gunsmith. Thanks for the help!

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Re: Help!! AR 15 experts..

Post by miker84 on Mon May 02, 2011 10:46 pm

Was the upper/barrel assembled when you got it?

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Re: Help!! AR 15 experts..

Post by staples on Mon May 02, 2011 11:06 pm

No, I bought all the parts separate and put it together myself. YHM 20 inch barrel, handguards and gas block, DSA stripped upper and the bcg out of another rifle. I double checked everything when I finished and all seemed well.

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Re: Help!! AR 15 experts..

Post by SubGunFan on Mon May 02, 2011 11:18 pm

Staples...... since you built the upper (the hard part), you have more AR build knowledge than most (including me - have seen barrels installed, but not done one myself - yet). I would check the barrel nut torque. Remove the barrel and start over. Torque the barrel nut PRETTY tight to get the gas tube openings to line up. Also, MAKE SURE the gas tube is not canted to one side in the upper.

If all else fails................... Use a BIGGER hammer...... Smile

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Re: Help!! AR 15 experts..

Post by staples on Mon May 02, 2011 11:24 pm

Ok thanks, I will take it down tomorrow and start over fresh...and I will be sure to use the 3lb hammer this time ! yell

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Re: Help!! AR 15 experts..

Post by rsm688 on Tue May 03, 2011 12:09 am

SubGunFan has been hitting all the points that I could come up with either (although I am pretty exhausted, I will have to reread the thread tomorrow and see if I can think of anything else).

I would definately start over with the upper and torque everything down right again. If that still doesnt work then you very well might have an upper that is slightly out of spec. You have eliminated the lower, ammo, magazine (I am guessing you tried more than 1 mag), and the BCG which leaves very few parts to be causing problems. If after re-assembling the upper if you still have the problem I would throw down some money for a new stripped upper (shouldnt break the bank).

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Re: Help!! AR 15 experts..

Post by titleiiredneck on Tue May 03, 2011 12:42 am

Sounds like you may have a canted gas block or possibly a leak in the block. As if its not alligned with the gas port in the barrel or possibly leaking from around the gas tube ect.. See if you have any carbon build up around these areas, another trick is to take a white kleenex and wrap it around the block, barrel and tube to see if it gets black. If its black or grey "not from the metal but carbon" then you have a leak!

Another idea is that you may have a mis-alligned barrel nut causing your tube to not be alligned with the "hood scoop" on the bolt. Try marking the tube with a black permanent marker and cycle the bolt, if its shiny on one side then its misalligned.

If all else fails then you will need to measure the od of th gas port in your barrel to see if its in spec, I have seen where they are a thou or so under causing not enough gas. This is a easy fix if you have a drill press or mill and a nice vise/barrel block and work your way up one size at a time till in spec going slow with fluid so you donot burr the inside of the bore or drill too far.

Also check the gas blcok as it may have a screwed up gas port "under sized or not drilled correctly.

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Re: Help!! AR 15 experts..

Post by titleiiredneck on Tue May 03, 2011 12:49 am

barrel gas port size should be 0.093 to 0.096 if 20"

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Re: Help!! AR 15 experts..

Post by miker84 on Tue May 03, 2011 7:19 am

OK, I'll pile on too. Sounds like an alignment issue. That's why I asked if the upper was assembled when you got it. Drilling the gas port is probably the last thing I'd do, altough an incorrect port size is possible.

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Re: Help!! AR 15 experts..

Post by critt77matt on Tue May 03, 2011 3:52 pm

could the buffer spring be too stiff. some how you got a 308 spring or something. If you have a different lower try it on and see.
Also to check gas flow you could plug the chamber and blow air into the muzzle and see if it is coming out the gas tube and check for leaks around the block.
She is good and lubed up I assume.

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Re: Help!! AR 15 experts..

Post by staples on Tue May 03, 2011 9:28 pm

Thanks all for the help, here's where I stand. I got home today and completely disassembled the upper and put it back together making sure everything was nice and tight like it needed to be. Verified the gas block and gas tube were line up correctly. I then completely cleaned and lubed up the upper very well including the bcg. Shot it and it still is short stroking. Tried it with different ammo, mags, bcg , different lower, and it short strokes with everything. Ok so the two things I did try that were suggested.I wrapped the gas block in tissue as suggested and there was a blackish grayish spot right where the roll pin goes into the gas block and just about the same diameter as the roll pin. Is this normal? Also did color the gas tube with a permanent marker where it meets the "hood scoop" and shot about 10 rounds and when I removed the gas tube some of the marker had been scraped off of the top of the gas tube...once again is this normal? Thanks again for all the help, I went ahead and ordered another gas block and gas tube btw.

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