Magwa Posted July 9, 2013 Report Share Posted July 9, 2013 Ok if I have it right a F marked FSB is for a flattop reciever and one not marked with a F is for a regular A1 reciever so I bought a clamp on from armalite for my dissy build the upper is a flattop but the clamp on FSB does not have a F marked on it it has a K1 marked on it so how much off will a non F marked front sight be can I get it sighted in? or am I screwed Quote Link to comment Share on other sites More sharing options...
blue109 Posted July 9, 2013 Report Share Posted July 9, 2013 If it doesn't work out for you I'll take that FSB off your hands for my A2 dissy:) Quote Link to comment Share on other sites More sharing options...
Magwa Posted July 9, 2013 Author Report Share Posted July 9, 2013 (edited) That is the point this FSB may not line up right with a A2 that is why I am asking but if I go another way you will get first option... I also have a A2 upper here is some info that explains it ALL GI SPEC CARBINES need an .04 inch higher front sight point. Doesn't have a thing to do with flat top or one piece upper. The Viet Nam era XM177s had an .04 inch higher front sight point. The only difference was that in the early days it was the front blade that was higher, not the base itself. Notice I said GI spec; because the aftermarket has played games w/the sight specs. The rear sight height dimensions on the M16, M16A1, M16A2, and M4s are all exactly the same, so long as the detachable units on the M4s are Colt, or other GI height units. The shorter sight radius of the carbine is what requires the higher point. In the earlier times, it was easier for Colt to simply use a hiigher post to accomadate the need on the relatively few short barrel pieces they were turning out for the Armed Foces, and civie market. When the M4 was adopted as the standard Army weapon someone (Colt? Army Ordnance?) decided that it might get confusing for Army repair shops to have to keep two differnt front sight blades in stock and heve to depend on workers there to decide what to use on what piece, and the F base was created. That way, they only need to keep one height front blade in stock. Up until recently, the bulk of the aftermarket avoided having to use a higher front sight point on their M4 type clones by making the rear sight bases of their clamp on units .04 inch LOWER than Colt and GI spec units. That let them use the standard rifle type front bases, and standard height front posts. Lately. more and more of the aftermarket barrels are coming out with F height bases (not always so marked), but so far as I know, the major aftermarket players like Bushie, DPMS, Stag, etc. sre still using standard bases w/ rifle height blades on their carbines, assuming you'll put one of the aftermarket sight units on your piece. If you do, you'll be fine. but if you mount a Colt or other GI spec unit on such a piece, you're probably going to either have to unscrew the front blade so the half the adjustment wheel is sticking up above the base, or replace the front blade w/a higher unit such as sold by Bushmaster, DPMS, and yes, even Colt. And if you're building a KISS carbine, w/an "old fashioned" one piece A1 type upper, you will certainly need a higher blade even if the Bushmaster catalog doesn't tell you that. Edited July 9, 2013 by Magwa Quote Link to comment Share on other sites More sharing options...
blue109 Posted July 9, 2013 Report Share Posted July 9, 2013 Good read! I didn't know about the different height aftermarket rear sights..nor have I ever seen one marked. Quote Link to comment Share on other sites More sharing options...
Magwa Posted July 9, 2013 Author Report Share Posted July 9, 2013 Yeah since it effects carbine mine will be fine because it will be rifle length sight radius. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.