Help diagnose this CMMG

D

dvdcrr

New member
ok my buddy bought a 18" stainless bull free float CMMG upper in about 2012. Complete factory free float varmint upper When he first got it it was short stroking. We took it down and it appeared that the gas block was not centered on the gas port when the sxrew was cinched into the dimple. Do you think it is likely that the dimple was indexed improperly? That is kind of what we thought but now looking back, they had to have used a jig right? That makes me wonder if maybe it was just a misalignmmet of the block.
How woild you go about fixing this?
 
The pilot hole for the gas block set screw is also the hole for the gas passage. Loosen the set screws, pull the gas block forward and measure the distance from the barrel gas port to the barrel shoulder. Compare that measurement to the distance between the set screw hole and edge of the gas block.

Also use a sharpie to mark a line on the barrel shoulder that points to the gas port. When you reinstall the gas block, the gas tube should be centered over that line.

Check the bolt carrier key for gas leaks or looseness.

Check the bolt gas rings to make sure they aren't loose inside the bolt carrier.

Personally, I don't like set screw gas blocks and use clamp-on or pinned gas blocks.
 
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