Originally Posted by coronadrinker85
the A2 front sight does work with a flip up right?
With the old A2 front sight base on a flat top (A2/A4) upper there might be trouble zeroing with milspec height rear sights, flip up or whatever. The front sight post will have to be unscrewed pretty far, often to the point where it's wobbly.
DPMS, Oly, Bushmaster, ArmaLite and others use the A2 FSB on their flat top uppers when they should use the taller milspec F-marked FSB. I ran in to this problem putting a used Colt carry handle on my A4 ArmaLite upper. Fortunately there's a cheap fix by installing a $6 Bushmaster 0.04" taller sight post.
The other option is buy a commercial height rear sight which aligns properly with the A2 FSB on an A3/A4 upper but I think it makes more sense bringing the front sight up to spec so you can use standard rear sights.