F-marked FSB

[mike01ta]

Hi. What is the difference between an F-marked base and one that isnt? I know they are for flattops but that is all I know. I just bought a new RRA CAR-15 A3 and it does not have an F mark on the FSB. Will this cause compatibility issues with anything?
Thanks,
Mike

[Robb Jensen]

You may have some zeroing issues using a non F FSB, Bushmaster makes a taller front sight post to remedy this is .020" or .030" taller.

[Akoni]

Hi. What is the difference between an F-marked base and one that isnt? I know they are for flattops but that is all I know. I just bought a new RRA CAR-15 A3 and it does not have an F mark on the FSB. Will this cause compatibility issues with anything?
Thanks,
Mike

I think the difference between the F and non-F FSB is something like the F is .040" taller. Colt developed the F FSB for use with A3 upper recievers. A problem *may* arise when trying to zero irons on an A3 with a non-F FSB. In order to achieve mechanical zero you could run out of elevation on the front sight post. As posted above, Bushmaster sells a taller front sight post to alleviate this.

Maybe RRA includes the taller sight post already?