orrbull, it will barely cover it if it's a midlength.

If you have a longer gas block (like a Daniel Defense, YHM, or MI, they will be longer, which take up more space on the barrel. I like the Stag lo pro and the Troy lo pro... as well as the PRI> These are all smaller in profile along the barrel, as well as being low enough to clear the rail on the bottom of the tube.

Just fyi.