I have a Rock River Arms standard detachable handle with A2 rear sights on my CMMG upper with a fixed front sight marked "F". I am a bit confused on the issue of the height of the post not matching up with the rear sights. Do I have a correct combination, or will I have to order for a different height post?

I guess I'll find out next weekend when I can finally break in this upper. Hoping to find out in advance before I take it out to the range.

thanks,

Yes, you have the correct combination.  The "F" designates a FSB that works with a flat top upper, which is what you have if you are using a detachable carry handle

Quoted: Yes, you have the correct combination.  The "F" designates a FSB that works with a flat top upper, which is what you have if you are using a detachable carry handle

The F FSB or taller front post are designed to work properly with mil-spec DCHs that have the rear sight base sitting higher than normal. AFAIK, only Colts and Leapers DCH's will require the F FSB or taller front post.

I boresighted my rifles at 50 yd and I had no problems adjusting the standard front post using DPMS DCHs.

The F FSB or taller front post are designed to work properly with mil-spec DCHs that have the rear sight base sitting higher than normal. AFAIK, only Colts and Leapers DCH's will require the F FSB or taller front post. I boresighted my rifles at 50 yd and I had no problems adjusting the standard front post using DPMS DCHs.

Assuming the above is true, how do BUIS's fit into the picture?  I'm told there is only one height for all BUIS's.  So is this height the same as Colt's and Leaper's DCH?  Or is this height the same as all other DCHs?

Quoted: The F FSB or taller front post are designed to work properly with mil-spec DCHs that have the rear sight base sitting higher than normal. AFAIK, only Colts and Leapers DCH's will require the F FSB or taller front post. I boresighted my rifles at 50 yd and I had no problems adjusting the standard front post using DPMS DCHs. Assuming the above is true, how do BUIS's fit into the picture?  I'm told there is only one height for all BUIS's.  So is this height the same as Colt's and Leaper's DCH?  Or is this height the same as all other DCHs?

I think most BUIS's are designed to work with the standard front posts/FSBs. It'd be kind of awkward to make all the BUISs only work with the F FSB or taller front post, since I think many issued M16s/M4s still have the standard FSB? I'm not sure if all mil-issued M16s/M4s have the F FSB.

The only way to tell for sure is try it at the range. Using a center hold (tip of front post is in the middle of the bullseye), if your shots are still high and your front post is practically coming off the FSB, you will need a taller front post.

Actually, the ARMS sights are designed to work with the Mil-Std F marked FSB. I had to replace the posts on my Bushy flat tops with the taller posts. If you have an F FSB, it should work with most BUIS, as this is what most are designed for.

Detachable carry handles have elevation adjustments built in. There is no need to change your FSP if you have a DCH. Now AR's buis WITHOUT elevation adjustments will require a new FSP, since they are as high as the detachable carry handles. The LMT, and DPMS do not require a new post, because they have elevation wheels built in too.

Oh, and unless your RRA DCH is the same height as a Colt, you may or may not have issues. Since you have the ability to adjust elevation with the A2 rear, you maybe ok...only one way to know for sure!