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Posted: 9/18/2007 6:08:03 PM EDT
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I was building an upper and I had a bit of a problem with gas tube alignment. It was a CMT receiver with an LMT 9.0 rail, carbine lenght gas tube from Colt and one of Denny's VCQB barrels. Long story short, even after multiple adjustments to the barrel nut, the bolt carrier would still make an audible and tactile "tink" when it hit the gas tube and you could see the carrier rise and rotate slightly when it engaged the gas tube. I tried marking the gas tube with a black marker to see where it was making contact with the key...it was on the bottom and right, at somewhat of a diagonal. So, more adjustments, more adjustments, and finally I just gave up and put it all together. It passes the carrier drop test and the carrier will close fully with very little resistance at about a 30-45 deg angle...but that "tink" and carrier lifting and slightly rotating is still there. Am I missing something? Is there a trick to aligning the gas tube on an AR? I was advised to bend it once it was installed with a screwdriver to make it fit the key...don't think that is a good idea though. |
| When I assemble an upper, I use my bolt carrier with a #16 (.1770") drill bit inserted point first into the gas key as an alignment tool. The drill bit fits firmly in the gas key, and is used to check for interference with the teeth on the barrel nut. The drill will hit the teeth of the barrel nut, as the bolt carrier is moved forward towards the chamber, if there is an alignment issue. Once the drill passes the barrel nut without hitting the teeth, install the gas tube. Most of the time, if you don't have a tweaked gas tube, the key will not make side contact like you noted. If you suspect that your gas tube is bent on the carrier end due to over zealous adjusting, get a new one and try again. |
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