I am putting together an A4 with scope to replace my A2 next service rifle season. I have a Bison Armory SR barrel, CL float tube and Bushmaster Upper. I am trying to figure out how I want to configure the gas block.

I have several gas blocks, a cut FSB, two A2 FSB and an A4 F marked FSB that can be used with the float tube. I want to be able to swap to a carry handle to shoot irons but mostly will use a scope. Can I use the A2 FSB?

One of the A2 sight bases have the post higher. I suspect the previous owner used it on a A4. I figured that could work since I planned to put a set screw under the front sight post to eliminate wobble. I figured the A2 base would be slightly lower and may show less in the scope.

With rifle length sight radius, the only difference the F makes is how high the deck is. The base of the post will look sunk in a little.

Get an “F” marked front sight base and use it.  I have one on mine and it does not affect the sight picture.  I also have a carrying handle zeroed for the rifle in the stool.

Dan