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3/3/2008 2:13:23 AM EDT
When is a "F" marked front sight base used? Is it used in conjunction with A3 uppers or only A3 uppers on M4's? Does it work with 20" rifles with A3 uppers?

Thanks
3/3/2008 5:51:56 AM EDT
[#1]
It works with everything.  Some combinations of barrel, upper and rear sight require more elevation adjustment than a normal FSB can provide.  The shorter the sight radius the more likely it is to be an issue.  In these cases you either need an F marked FSB or an extra tall front sight post.  Since you cannot easily replace a FSB, getting a barrel with an F marked part in the first place avoid potential problems.
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