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Posted: 3/31/2009 4:06:17 AM EDT
| Is the gas hole in the barrle the top dead center of the barrel? |
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After they install the Barrel Extension and drive the index pin it, the index pin acts as the TDC index and it is used as the index to drill gas port at TDC.
The index pin is used to line up the barrel (index it) with the upper receiver. It should all line up, but of course poor QC, mistakes, wear, etc sometimes they don't. Either the gas port is off OR there is some slop between the index pin and the slot in the upper receiver and it lets the barrel tilt a few degrees. The later is more common and can be fixed with shimming (filling in the slop) the index pin in the receivers slot for it. |
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