Home AR-15 AR-15 F Marked Front Sight Block (FSB): Does It Matter?

AR-15 F Marked Front Sight Block (FSB): Does It Matter?

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Does the “F” marked FSB matter?

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20 COMMENTS

  1. I recently bought a palmetto freedom rifle kit. It has the F front sight block. What is the block and groove for on the very bottom of it? Flashlight? Bayonet? No reason? I am new to the AR world and I am trying to learn as much as possible. I have owned pretty much all bolt action rifles, revolvers etc. Any info would be greatly appreciated. Thank you.

  2. Mrgunsngear Channel I have a Troy Foldable Front Sight that, for the 50 yard sight-in, the post sticks out a lot. To the point to where the post Bottom flange is kinda high off the platform. I just ordered a .40 and a .60 tall posts from Wyndam Weaponry. Hope that fixes that issue

  3. So, if one has a non-F-marked FSB, does a flip-up rear sight that goes to standard AR sight height match up "better"?  I'm looking for a flip-up rear sight to replace the one on my commercial (I assume) carry handle, which I removed to accommodate an optic.

  4. I guess if you have standard A2 receiver with a F marked front sight base you could have issues with elevation. It would be rare but it could happen if you tried to reach out 500 meters or more. That would require to crank the front sight post all the way down.

  5. I heard the reason the rear carry handle was raised was not because of extra material on the upper needed but because of the shorter sight radius on carbine length barrels, therefore since Colt manufacted barrels and fsb(s) as one piece they just used longer front sight posts. But the key is it is a wives tales that Colt used more material and that a designer poked a hole with a lead pencil in the upper (adding more material). Military style high "F" marked (added height) vs standard front sight base height is due to shorter sight radius.

  6. THANK YOU SO MUCH !

    I have both an F marked and non F marked Colt AR-15 A4's. I also have an M4 6920 which is of course F marked. I knew there was a difference but I didn't know what the details were until now. Your right, the F marked AR-15 A4 and the M4 have the same sight post height area while the non F marked AR-15 A4 does have a slightly lower sight post area. I never noticed until now. After I watched your video I busted out all 3 rifles and lined them up on the dinner table and they are exactly how your video explains !

    I have had ZERO trouble sighting in the non F marked AR-15 A4 at 100 yards. I was always a little mental about my first AR15 A4 not being F marked even though I never had problems sighting it in but now I'm glad to know the exact differences.

    Thumbs up !

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