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Posted: 1/22/2008 2:53:23 PM EDT
| I just pulled the carrier and the gas tube, the key on the carrier looked and was torqed nice and tight. The gas tube was clean, but i noticed when i removed the top hand rail guard their was some black carbon build up inside where the hand guard fits (around the gas tube), next to the Front sight???? |
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What DPMS upper? Is this one with a FSB or gas block. Have you checked both the gas tube and carrier key for flow tests? If a gas block, could be that it's not indexed with the gas port. Regarding the carrier key, could be that carrier port and end of key passage are misaligned. On the bottom end, can you lock the bolt back by hand (read the catch rises in front of the bolt face and retains the bolt back via the face of the bolt, and not the carrier. Have you checked the trigger/disco tail for hammer wedging? Also, was the rifle correctly cleaned (read use of a chamber brush and all copper solvent removed before the upper bearing surfaces, including the buffer and spring, lubed with CLP. Regarding the buffer spring, did you check the end of winds to confirm that there is not a end of wind bur scrapping down the inside of the tube. Simply, with the lack of information you have given on the rifle and it's history, about the best I can do is suggest that you send you the upper/rig off to someone so they can get it in there hands to trouble shoot it. |
| Its a FSB, i've checked the gas tube for flow, and the carrier key using a straw, seems fine. Iv'e also tried a different lower, same problem. so its defenitly the upper. I guess i could re-stake the gas key, any more suggestions???? i really apperciate everyones help, im new to the ar, and just want to get this sucker shooting. |
| I wonder if its the magpuls, i have seen some people with problems here recently. Its not really ftf, just wont hold the bolt open. I tried 3 magpuls, same with all three. But there all magpuls???? Also ive got a buddy with a DPMS varmit uppper and his magpuls (same manufacture date as mine) holds his bolt open??? |
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Don't screw around with the carrier key, Just borrow someone else's B/C from a working rifle and re-test. If the upper still have problems (both on your and other lowers with know working mags), then box it up and send it to DPMS. It could be a tight/rough chamber or gas port problem that they need to correct. |
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For testing, using different B/C's will not be a problem since you will be only firing the rifle for a few rounds. As for long term effects, the bolt mates to the barrel extension through a rifles normal break-in period, and when you start swapping bolts (read run the different combo's for thousands of rounds), each bolt will try to mate with the barrel extension, and it can cause premature service life of the parts. As for the carrier, it is not a problem of playing mix master with them from rifle to rifle and really the only concerns here is just checking the key alignment to the gas tube each time a new carrier is introduced to a rifle (upper). |
The length of the receiver extension (tube cavity depth) determines the spring and buffer lengths. Regarding springs, there is either in-spec springs, extra tension springs, over often round with cheap stock sets, a full length spring that has been clipped to carbine length, and since the spring coil is the wrong size (read too small) the spring is too weak to begin with. As for buffers, if the upper chamber and gas port are in spec, then a standard buffer (carbine in this case) is enough weight. As for the heaver buffers, they are used to slow the fire rate down on full auto weapons, used to compensate for heaver ammo (slow the unlock down since the port pressure will be higher due to the use of slower powders). Or used as band-aids when the barrel parts (chamber/gas port) are not in spec (to slow the unlock down). |
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