Originally Posted by MikeJK
W/ all the "my sights don't line up" threads that end up being the fault of a half ass railed gas block you'd think people would stop purchasing ARs w/ those ugly railed gas blocks.
Yeah my first AR build had an ArmaLite upper with the low rail gas block so I got ArmaLite's clamp on FSB that got it to the right height for their own rear sights. Trouble was they used the commercial height like Bushmaster, DPMS, Oly and lots of others - not the milspec height for a flat top (thus the F marked FSB that Colt, BCM, DD, LMT, Noveske and the better ARs use).
It was frustrating trying to zero the irons until I finally found out about BM's tall front post for Colt height rear sights and now I can use any milspec rear sight. Funny, that one thing opened my eyes to going with quality ARs from then on. If that little thing was wrong, what about the really important things!
Could be the same thing going on here but I bet moving the front MBUS to the quadrail will fix the problem quick, both sights should be milspec height then.
The opposite can happen too - if you get a BM carry handle or rear sight and try to use it with a milspec front you have to crank the sight post way down into the FSB and maybe get it to zero. At least with a BM carry handle you can reindex it about 14 clicks below 6/3 to raise the peephole to milspec height.