RRA 10.5" SBR with fixed FSB sights compatilibty.

AR/M4 AR Technical Discussion
1

I’m finally moving forward with my 9mm SBR build. I have a question regarding the RRA upper.

The upper I’m getting (its on a post truck right now) is their 10.5" flat top configuration with fixed FSB. Will I be able to zero the upper utilizing Troy Buis and RRA FSB? Or do I need an F marked FSB?

Thanks in advance

Paul

2

That’s an interesting question.

I’m also looking at getting a RRA 9mm SBR (mostly so I don’t have to engrave my Colt) and the thought of sight compatibility never even entered my mind.

3

Can anyone comment on this issue. I have a DD rail waiting to go on and I’d like to know if I have to swap the FSB before I install the rail.

Thanks in advance

Paul

4

Nobody is using Troy buis with RRA fixed FSB?

I guess I’ll have to be a guinea pig:( I was hoping to find out before I install the rail because swapping FSB with DD 9.5 rail is pain in the ass.

Paul

5

Some RRA FSBs’ are F height, if yours isn’t a taller front sight post is like $6 from Bushmaster.

6

Thanks GotM4. I saved the picture of FSB height difference that your posted a while back. I’ll measure the height on existing and see how tall it is.

7

You can bzo a standard FSB with buis’s on a flat top w/out the .04" taller post. It just depends what sight you’re using. I did it using ARMS 40’s on one of my flat tops with standard FSB & it shoots fine. If you don’t want to chance it then by all means order the taller front sight post.

8

I would love a 10,5 upper but must be 5.56 or 6.8