M16A2E3 Experimental Rear Sight

Have you ever seen an M16 like this before? Look closely. Right below the detachable carry handle’s rear knob, there is a piece of metal on the side of the upper receiver. Weird right? Well it is actually an experimental rear folding sight. It folds down flat and the carry handle has a notch to accommodate the stowed rear sight.




According to this book, the folding rear sight has a windage adjustment on the right side of the sight.


rear sight


I am not sure why one would need a back up rear sight when they have a carry handle rear sight to begin with. Of course you could remove the carry handle and mount a red dot, but I do not think that was Colt’s intention when designing this rear sight.

Nicholas C

Co-Founder of KRISSTALK forums, an owner’s support group and all things KRISS Vector related. Nick found his passion through competitive shooting while living in NY. He participates in USPSA and 3Gun. He loves all things that shoots and flashlights. Really really bright flashlights.

Any questions please email him at nicholas.c@staff.thefirearmblog.com


  • Lance

    This came from the defunct ACR program in 1990. In many way it served as a forerunner of the current M-16A4 and M-4 series of weapons.

    • Anonymoose

      And it has the same gas block as the LE6940! At least something good came out of this.

    • This variant predated the Colt ACR.

    • Phil

      Correct but that ACR program starting in about 1980 (or even earlier, it was right at the end of the small calibre evaluation) and was run by PM-Small Arms out of Dover NJ in parallel with the Marine program that gave us the M16A2 eventually (and a superb range at Fort Benning). I saw that sight at Colt when I was there and it was intended to go under the optic (Elcan at the time, but later a Trijicon) as a back up iron sight was a requirement of the ACR.

  • John

    M16, A2, E3, V4, ah, ah, ah.

    • PK


  • Anonymoose

    Seems like a neat idea until you realize it’s non-adjustable and that those are Weaver rails on top. I’ll stick with my modern folding BUIS, thanks.

    • Christian Hedegaard-Schou

      Except it is adjustable.

      I know that because I actually read the article.

      • Soless

        Feel free to drop the mic any time.

      • Billy Jack

        Christian’s replies are deadlier than a M16A2 Enhanced Rifle.

      • PK

        He’s already dead, stop!

  • Martin T√∂refeldt.

    What is the book title?

    • “Black Rifle II” by Chris Bartocci

      • Martin t√∂refeldt

        Thanks for the info.

  • DataMatters

    Some idiot would clip his sling to it and rip that thing right off. After he lost the carry handle…

  • Cap’n Mike

    According to Black Rifle II, it came from the Military s ‘Future Rifle Program’, the goal of which was to design an integral rail type mount on top of the receiver onto which could be attached a scope or any other kind of optic sight.

    It was given the name ‘M16A2 Enhanced Rifle’ in April 1984 and was delivered to the Army in April 1985.

    Very cool.

  • DW

    Would make a great BUIS for KAC URX handguard

  • jerry young

    I left the Army in 1973, joined the national guard in 1974 through 1978 we had the M16A1 the carry handle was not removable, today I own AR 15’s and prefer the flat top with red dot sights and offset iron sights for backup, I never liked the carry handle, I find it easier to sight with a flat top with normal iron sights than one with a carry handle!

  • Graham2

    It’s a shame they didn’t think to have a smaller backup sight under this one, for when things have really gone bad! Sort of like Russian Dolls, there’d always be just one more…

  • DanGoodShot

    Its a back up for the back up of the back up. Ok… got it.