Originally Posted by xRacerX75x
Would it have negative effect if I used a RRA rear sight and a magpul front sight... aside from it looking a little funny?
Probably not, but there are some manufacturers like ArmaLite, Bushmaster, DPMS and others that use the old A2 height front and rear sights on a flat top receiver instead of A4. In that case you need to either use their sights to be able to zero the irons or buy a taller front sight post then use the standard height rear sights like Magpul. (I went through this with my ArmaLite upper but it was the front sight that was low, in your case it could be the rear.) I think RRA uses normal A4 height sights but be sure before mixing with another brand.
As SSGN_Doc said you don't want to put the MBUS on a railed gas block which from your avatar it looks like that's what you have.
Post a close up of your carry handle if that's what your talking about. Make sure we can see the sight area and I or someone else can tell you if it's A2 or A4 height.