are you looking for a gas block with a rail or just a low profile gas block that can be mounted under a free float? Daniel Defense had a decent low profile gas block that will fit under rails for the light weight barrel. There are others out there also with rails on them (yankee hill). Just remember that the rail will get hot if you do alot of shooting so a metal flip up sight would need to go on it.
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There's nothing like the fact that you can take educated professionals with everything on the line and add a little booze and they act like juniors in HS.