"WHY DOES ARMALITE CALL THEIR FLATTOP RIFLES "A4" INSTEAD OF "A3" LIKE OTHER MANUFACTURERS?
Because ArmaLite tries to follow military designations to avoid confusion. The M15A2, for instance, is a commercial version of the M16A2 rifle, and is not capable of automatic fire. The M16A3 model is like the M16A2. The only difference is that the M16A3 is equipped with semi/auto settings on the selector, while the M16A2 has seim/burst settings. The military M16A4 is like the M16A2, but is equipped with the flat topped upper receiver equipped with the Picatinny Rail. Other commercial rifle makers adopted the A3 designation for their flattops without knowledge of the military plans." copied from armalites home page
Yes, this item will fit on any rifle upper with military type picatinney rails
If you are interested please make e-mail me before tomorrow night, I will be out of town until the 24th and will not be able to respond to e-mails