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Posted: 9/17/2006 8:54:06 PM EDT
| Just need to confirm if there is a difference in front sight base (Height) between A1/A2's and the M4--does the M4 flat top have a shorter front sight base? |
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"F" marked (or not marked) M4 spec front sight bases will be about 1mm (~0.040") taller than A1/A2 spec front sight bases. Just because there is not an "F" stamped on it, that don't mean it ain't an M4 FSB. LMT makes ONLY M4 spec front sight bases, so they have no need to stamp an "F" on them. The "F" stamp is a colt thing, to differenciate M4 from regular A2 front sight bases. Other companies in the industry have simply followed colt's convention of stamping the "F" on M4 height front sight bases. If you end up with a Mil-Spec height backup rear sight or carry handle and an A2 height front sight base, there are extended height posts available that correct the mis-alignment. |
Indeed. But this remedy makes the Front Sight Post more prone to damage since it sits higher between the ears. Although it will work, I prefer getting the correctly matched FSB and Receiver. |
Common misconception. The actual forgings used to make A2 or M4 front sight bases are the same. Therefore, the ears are the same height. The only difference between A2 and M4 is that the SHELF is machined taller. This allows the same sight post to be used in either with the base of the sight flush with the shelf on the sight. If you measure how far the two ears stick up past the front sight post on M4's and on an A2 with extended post, they will be roughly the same. Therefore, all M4 sight posts sit closer to the top of the ears, no matter which FSB. Also, all A2 sight posts would be better protected when used at the A2 spec height. |
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Really? So buying the taller sight post would just position it roughly in the same height relative to the ears as an M4 FSB with the standard sight? I think I'm confusing myself now. |
Correct. Also pointed out above is the fact that the taller sight post would be theoretically weaker because it's longer. I'll add that if you are abusing the rifle enough for the difference in sight post strengths to matter, you have bigger problems and should call for air support. |
I actually damaged a front sight post and had to replace it. If there's one part that would end up getting damaged, it'd be my sight. It's just my luck. 
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True. I think my main complaint is that the one I got from Bushmaster is not simply a taller A2 post. It is about .01" narrower and doesn't have much of a taper at the base. I like the thinner post from an accuracy point of view but I'd concerned about having it on a weapon kept for home defense. |
Gee, that's the exact same "bandaid" that Colt has used on all their carbines and SMGs all the way from the XM177s up to the advent of the M4 type F base, which was created simply because the Army didn't want their armorers to have to stock two different front sight heights, and risk putting the wrong blade height on a piece in for rebuild. My SP1 carbine came w/an .04 inch higher front sight blade in 1978. The "it's for the flat top" mantra is total bullshit. It's for all carbines; and it don't mean a damn thing whether it's a higher base or a higher blade. It all works out the same. It has to do w/the shorter sight radius on carbines, not anything else. And if you don't believe me, send me $5 for my time and trouble, and I'll send you the ROUND post that came on my SP1 carbine along w/a round M16A1 post that's .04 inches shorter than the carbine post.  Edited to Add: Oh, by the way, you can still buy the "bandaid" from colt (part #SP64665) if you don't ike Bushie's band aid.  And of course it's narrower than the rifle blade. It's closer to the eyes, and so gives the same visual appearance on target of the rifle blade on a 20' barrel. You're worried about the thinner blade getting bent?? What the hell do you think the wings on either side are for?
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Give me some time and I'll post a pic of where the top of the post is relative to the ears on the FSB. |
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does anyone know if the taller .04 post is absolutely nessasarry to get enough elevation on a non f-marked fsb? i have a trijicon front sight post , which is .02 taller than a plain a2, and i just sent my upper off to bushmaster to get an a2 upper switched to a flat top. |
Absolutely not. The only way to be sure that you'll need it is to go to the range and zero the weapon. If you can't zero it because you run out of elevation adjustment then you know you need the different post. |
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