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BUIS with standard FSB


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Hi all, Here's my question. What rear buis options will work with the standard FSB. I am swapping out my carry handle upper for a flat-top upper and wondered if there are compatible rear sights, or do I have to go the new gas block route, with a new front sight as well? If this is not a violation of protocol, I will obviously have a gently used carry handle upper for sale, after the surgery. Thanks, in advance for any and all help from the forum. Red.

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All of them... 99% of the BUIS are designed to line up at the same height as the FSB. All front sights; handguard mounted, gas block mounted, FSB, are all supposed to be at the same height. This way the rear sights can always be the same.

The only types of sights I would be weary about, are the ones that state they are "micro" or "low profile". I have a set of Troy Micro BUIS on an AR, and I'm not 100% sure they are the same same height as the original BUIS. I never measured them to confirm or deny this.

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There's a 0.040" difference in the height of a standard front sight base and the "F" marked front sight base.  F marked front sight bases were developed for the shorter M4 Carbine, over the M16A2.  The difference in the sight base height on the shorter carbine was necessary due to the change in sight radius.

No matter which front sight base you're using, F or standard, you can make up the zero difference with the standard front sight post.  Only thing is, it might be sticking up a little further, or sunk a little lower, that what looks normal.

You never stated what the configuration is on your particular AR-10.

post-71-136297272084_thumb.jpg

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Rifle started as a carry handle (A2) upper that i bought from a friend. I bought the complete lower from Armalite. Shot it for awhile, decided to make it into a flat-top. Bought the stripped lower a month ago on sale. Accumulated needed tools etc, and will make the conversion tonight. 6 position stock, free float tube from Model 1, Armalite flat-top receiver, Armalite complete lower. Gonna glass it, add a BUIS, and use it as a hog rifle. I'll take pics before and after, and try to post them. Red.

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  • 3 years later...

The rail should not have contact with the front sight tower, if you're talking about the handguard.

 

As far as rear receiver height, and rear sight mount, you can adjust for that small difference via front sight height adjustment.

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