FSB height?

[Cooper1]

Hi All,

I have an Bushmaster M4 clone (A2 style) that I replaced the upper with a Henderson Defense flat top. I put a YHM low profile rear flip up on it and kept the original fixed front sight base. How do I know if I need a taller front post? I am limited to a 25yd range, so the poi seems ok... Looks like the FSB is marked 01 "something."

Thanks

[Auto-X Fil]

If it's not stamped with an F, you might want a taller post. You'll know if you do - the front post will be really high in the base, and can get wobbly. Here is an extreme case:

http://s1034.photobucket.com/user/BajaATZ/media/FrontSightPost.jpg.html

[Molon]

"F" Marked Front Sight Base


There is no difference in the overall height of an “F” marked front sight base and a standard front sight base. The only difference between the two front sight bases is the height of the sight “shelf” above the top of the barrel.


http://www.box.net/shared/static/uei1uar8kw.jpg



http://www.box.net/shared/static/2d520zm04w.jpg



The front sight post on a standard Colt front sight base will bottom-out in the sight well at approximately 24 clicks below flush. On an “F” marked front sight base the sight “shelf” is a whopping 0.040” higher than on a standard front sight base. That means you might have to turn your front sight post down approximately 6 clicks further with an “F” marked front sight base than on a standard front sight base. (6 whole clicks difference. Oh, the inhumanity!) So unless your front sight post is set at 18 clicks below flush with a standard front sight base, using an “F” marked front sight base on a 20" barrel will be a non-issue.



.....



You may find that once you have set your 50 yard zero or 100 yard zero, etc, the top of the base of the front sight post is now slightly above the top of the well in the front sight base. If this happens, the “0.040” taller” front sight post from Bushmaster provides a quick and inexpensive fix.


http://www.box.net/shared/static/kc9mgqaqvm.jpg



....

[Cooper1]

Great. Thank you for the clarification. My post base sits proud more than half its thickness, so I think I'll order a taller post.