I got this forend to go over an American Tactical gas piston upper. I knew it would not be a drop in application, but being a gunsmith, as long as I have extra I can always mill away what's not needed or in the way! The pic rail of the gas piston ended up about 1/16" above the forend pic rail. Not quite flush. The internal area of the forend had to be clearenced to allow the gas block to free float with the barrel. The gas piston drive rod fits nicely in the gas tube area. The gas plug required milling away 1 lug of the top pic rail just forward of the sight post opening, and still requires re...
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