I put on my FF RAS on my M4 barrel tonight, which of course required the removal of my front sight tower.  I've got the urge to put a gas block on now, but I'm not sure which one will work best.  I like the looks of the 4 rail gas blocks, but will they fit with the FF RAS?

Also, where the sight tower was removed, there's no finish on the barrel.  Should it be refinished somehow before I place a gas block over it?  TIA

Not sure what RAS means, so not sure if a 4 rail will work or not. You could get a single rail block which seems to fit most free float tubes. Depends on how high the rail is from the barrel. I had an M&A and it fit with my free float tube.

But as far as the finish goes, I would just clean it really good with some acetone, then cold blue it. It works better than leaving the metal bare.

Cerebus,

I know what your talking about, it should work fine. The RAS was designed to stop right where the hand guard cap normally is. This should allow the block to slip in place of the site tower. Dogcatcher223 is right just clean it and cold blue the metal.

Dogcatcher,

RAS stands for Rail Adapter System made by Knights Armament or KAC as a lot of the guys call it.