I've read numerous posts regarding POSSIBLE issues with flip up rear BUIS' (ie. ARMS 40) and the need to go to a taller front sight post on 16" carbines. I contacted ARMS today and spoke with customer service who informed me the ARMS 40 line was standard milspec height and would not cause a problem with the front sight. The person I spoke with did mention a particular maker was known to not always use milspec FSB's and a rifle from that individual maker may pose a problem.

So Arfcom, what say you? ARMS 40 on a RRA 16", good to go?

If you have a M4 height front sight base, you should not have a problem.  If you have an A2 height front sight base, you will need a slightly higer front sight post.  Bushmaster requires the higher post.  I have a 16" Bushmaster pre-ban A3 upper with a #38-EX Swan Sleeve on it, which includes the #40 BUIS.  Outstanding unit.  I use it for mounting my Aimpoint ML2 with a A.R.M.S. Comp II M68 quick release ringmount.  I cannot say enough good things about A.R.M.S.

Yup, BM was the maker he mentioned.