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Posted: 3/31/2007 2:45:18 AM EDT
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The barrel is a DPMS 20" stainless match with match gas block/sight. The replacement gas block is the four set screw variety of the PRI flip up sight. I never fired the rifle in its original configuration. I replaced the match gas block for a the PRI flip up gas block. My rifle is currently a single shot, with only one occurance of actual semi-auto fire. The brass is either not ejected or gets stuck in the ejection port on the way out. I removed the gas block and inspected the ports on the gas block and gas tube. It appears the two holes are not aligned when the roll pin is inserted. The misalignment is lengthwise by about 1/4-1/3 of the diameter of the hole size. Not having any experience with a stainless barrel, I noticed burn marks along the rear of the gas block outward. Any thoughts (besides don't buy DPMS)? Thanks in advance!  Forgot to mention: HSM 62 gr - about 20 rounds fired PMC 55 gr - about 120 rounds fired Fed 55 gr - about 20 rounds fired |
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Using a drill bit upwards in the bottom of the gas block, enlarge the gas tube hole to fit/align with the gas block passage (note: only enlarge the bottom tube opening, and not drill/make a new hole into the top of the tube). On the gas block to barrel, mic and mark the center of the barrel gas port to the barrel shoulder. Now mic the gas block to center of its gas passage. On some Gas blocks, the gas passage is set for installation of the front hand guard clip. If in this case, you are not using a front clip, then you would set the gas block slightly off the barrel shoulder the needed space of the hand guard cap, and then using the barrel shoulder mark you made, align the gas tube to the shoulder mark when setting the gas block. Now the last item to bring up, and really the first to check, is confirm that the barrel gas port is top dead center of the upper receiver. If the barrel was not installed correctly indexed, then when you go to index the front sight at zero, you will miss index the gas block passage against the barrel gas port, blocking the works. |
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It should be obvious that you must have the correct amount of gas taken from the port and delievered to the boltcarrier in a timely fashion. So, to insure the correct amount of gas, ensure a good seal at the start of this cycle. Next is to be sure the tube is without leaks and that the gas key is making a good seal as well, to both the tube and the carrier body. There must be a complete and functional system in place in order to have a functional reliable weapon system. Yeah if it is obviousily not working or fit correctly... change it out. |
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