ACOG with BUIS - Will only Troy fit?

[gtomax]

Read something about going with the troy rear BUIS if you run an ACOG as there's not much clearance there. Fact or fiction? Also, this will be on a flattop without a front sight post (railed gas block) so I'm guessing if I go Troy I would need their front sight as well to maintain proper plane?

Thanks

 

[RockyMtnTactical]

An ARMS #40 will fit under an ACOG. I've done it with both the ARMS #40 regular BUIS as well as the low profile ARMS #40.

You can see the ARMS #40 under the ACOG TA31 on this pic.

 

[MisterPX]

My YHM fits under my TA31

 

[Bartholomew Roberts]

The regular ARMS #40 with shaved aperture doesn't always fit under the ACOG. It is just tight enough that tolerances sometimes stack in the wrong direction depending on the mount you use (if you use the ARMS #19 mount, you will be fine; if you use the TA51 mount then maybe, maybe not; if you use the Larue low-ACOG mount then no way). If you used the non-shaved aperture then none of those mounts will work.

The ARMS #40L will fit just fine and is cheaper (though not quite as nice) than the Troy, if you need to save a few bucks.

Anybody's front sight post should work with anyone else's rear sight from a height/plane issue. It doesn't always work that way; but generally it will.

 

[HorseSoldier]

I've used a standard, USGI BUIS on my issue M4A1 with ACOG for a while. Fits just fine. Have also tried a PRI rear BUIS on the same rifle, also fits fine.

 

[gtomax]

Went with the troy rear and YHM flip up gas block mount front.

Thanks guys!