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Posted: 4/27/2008 3:34:14 PM EDT
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I have a 24" SS varmint bull barrel on a DPMS lower. Took it to the range for the first time Saturday - she shoots great but the bolt does not open to eject the spent case or to pick up a new round. No gas movement at all. I manually charge the first round, fire, then have to manually pull the charging handle to eject the spent case and load the next round. The bolt stays open with an empty mag in the well and without a mag in the well it will open and close normally. I checked the gas tube and it's all clear. I removed the gas block and noticed a carbon buildup in the shape of a half moon immediately behind the gas port on the barrel. Does this mean that the port in the barrel and the port in the gas block are not in alignment? I hope if one is out of spec it's the gas block not the barrel - any advice? |
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With the gas block/tube in hand, look up through the bottom/back screw hole to confirm that the gas passage and tube entry hole are aligned. With the half moon, the gas block to the barrel port is not aligned. If they where, you would have a full burn cleanly circled around the gas port. To get the alignment right, mark the shoulder of the barrel at the center of gas port, then align the tube with the mark. Also, mic the barrel shoulder to the center of the gas port, then the center of the gas passage to the back face of the block. It could be that the gas block needs to ride off the barrel shoulder a tad to get everything lined up correctly. Note: don't forget to apply loctite to the gas block allen screws or they will back out in no time (read cause a gas leak down the road). |
| Funny you should have the problem only I have a similar problem with a 20 inch DPMS bull barrel. The gas tube roll pin when inserted in the DPMS gas block puts the two gas holes out of line. Mount the gas block to the barrel and the two holes are approx 3/32 out. So gave up on that gas block and am awaiting a new gas block so we will see. Tried to build it using all DPMS parts but cannot get a dpms gas block from any of the above vendors. |
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