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Old 06-22-2014, 04:52 AM   #1
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Default Short stroke problem

A customer brought me a AR -15 that he built his self. He said it was short stroking. So I disassembled it and done gas checks, I also check to see if there was drag on the bolt and buffer tube. I also checked alignment on his gas block . He did have alot of tension on his delta rings from his forearms being slightly to long ,and I had noticed his gas block had slid forward. So I shaved a lil off his forearm and put it back together and test fired it and still same problem. Can anyone help. His barrel is a daniel defense. S&W lower and upper, magpul stocks and buffer. He didn't tell me were he got his internals. Any info would be great.

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Old 06-22-2014, 05:15 AM   #2
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if its a carbine tube check for rifle tube recoil spring and or rifle length buffer.

loose gas key is another issue area. ive had to redo bcg gas keys for friends on dpms rifles.

wrong diameter gas block can be an issue especially if its a off brand. check outside diameter of the barrel at the gas port and inside diameter of the gasblock.

take the bolt out of the bcg check for binding on the gaskey and gas tube as the carrier moves back and forth.

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Old 06-22-2014, 05:50 AM   #3
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I took the bolt apart and checked binding and buffer spring they r good I even put hos upper on my lower and same issue but my upper on his lower worked fine so I narrowed it down to some were in the upper

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Old 06-22-2014, 09:28 AM   #4
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Gas rings aligned?

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Old 06-22-2014, 10:18 AM   #5
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I have the same problem.

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Old 06-22-2014, 11:20 AM   #6
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I would pull the carrier take the key off . Get a couple new screws and put a thin coat of loctite on the base of the key, tighten it up and let it dry. Sounds like its leaking at the key . Gas ring alignment don't worry about . If it still malfunctions after that check gas hole size and make sure there isn't any burrs in The gas hole or gas block holes.
Is this a new upper or used ?

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Old 06-22-2014, 02:38 PM   #7
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I have disassembled the bolt and checked for leaks I proven the bolt out because I but my bolt in his gun and it would eject the shell but not extract another.before it wouldn't even eject the shell

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Old 06-23-2014, 01:05 PM   #8
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Possible buffer spring being too stiff--change to known good one to check. Too heavy of buffer. These however wouldn't prevent shell extraction as you've tested. Who makes the BCG?

Bad gas block drilling(oversized gas tube port) or it's alignment to barrel gas port.

I wouldn't think with a quality barrel like DD that they would drill too small gas hole, but I would check. Bad gas tube? Do you notice any odd residues around the gas block/tube, or barrel extension that shouldn't be there?

Don't worry about gas rings being aligned. Once installed in Carrier, those gaps close, that's why you have resistance when installing.

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Old 06-23-2014, 08:27 PM   #9
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I switched buffer and spring from my AR to his and it didn't make no difference I have never had this much trouble out of one im stumped

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Old 06-24-2014, 12:13 AM   #10
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I noticed you said you swapped Bolts(yours for his to test), but you didn't mention whether you swapped complete BCGs? It's possible there's a problem with his carrier, while his bolt is good.

Do a swap out of known good complete BCG to see if it clears up the problem. If not, you eliminated that aspect, which means there's a gassing problem since you swapped buffer/spring components to check.

I just thought of something. Have you inspected the interior of Upper Receiver for odd markings of severe rubbing. This would say the receiver isn't milled correctly and is putting the brakes on the Carrier from operating smoothly like it should. If you know the interior measurements of receiver, use digital caliper and compare with others. It may just be too tight.

Of course, we're like you---check this/that and eliminate before moving on.

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