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Posted: 6/14/2006 4:46:41 PM EDT
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Give me the low down on the "F" marked please. What are they on/not on, what's the difference between regular and "F", ect. I've looked and can't find this in ARF. |
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I believe they are made for flat top carbines. If you have an flat top, and a regular front sight base, and a BUIS, you can have difficulty zeroing. I had that problem with my BM Patrolman's Carbine with a LaRue BUIS. It zeroed witht he std FSB and post, but the post was screwed out so much you could easily see daylight below the post's base and the FSB housing. I never felt comfortable with that. Instead of going to the proper F-marked FSB I just added the taller front sight post and it easily zeroed. $5 vs a new FSB and a gunsmith to install. Having said that, if I were doing a build and spec'ing things out, I'd go with an F-marked base. |
Basically, there are two different standards in FSB height. "A2" and "F" "F" is roughly 0.040" taller than "A2" This comes from the early days of flattop receivers. The very first flattops were so thin that you could poke a pencil through the bottom of the picatinny slot and into the channel where the charging handle rides. I forget who it was exactly that demonstrated this. In any case, they raised the rail height 0.040" to thicken this up. That caused the rear sight on the removable carry handle to be too tall. The solution was to machine the FSB 0.040" taller to match. Viola, there's your "F" height FSB. Now in the commercial world, manufacturers made a removable carry handle that was simply machined down 0.040" lower so they could use an "A2" FSB on ALL barrels. Viola #2, mixed standards... So, you use an "F" height FSB with "Mil-Spec" height rear sights. You also use an "A2" FSB with lower "Commercial" height rear sights. If you end up with a mismatch of parts, there are taller front sight posts available to fix the problem or you may need to grind/file off 0.040" from a regular front sight post. Either of these solutions is likely to fix any mismatch of parts possible. |
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