I have an older Bushmaster XM15E2 with a non-removable carry handle. I got a great deal on a new ACOG ($949 at beyondguns.com), so I went ahead and snagged one. Now I'm just wondering what would be the best mounting option. Would prefer to keep iron sight functionality.
ACOGs are prism optics - you won't get much in the way of angle/position adjustability and have it be usable. Eye relief and parallax are a pretty narrow range on prism optics. Probably best off with Trijicon's mount, which I don't think maintains iron sight functionality. AR sights are already a good height over the bore, carry handle mounts are even further off. You might want to see about a cheek riser stock for your rifle - so you can get proper cheek weld / eye placement, rather than doing more of a chin-weld.
The carry handle mount for the acog is integral to the optic and part of the original design. Remove the picatinny mounting base and the dovetail fits into the carry handle channel. There should be a screw in the box to utilize for this method of mounting.
mylar17 has that right. and they include or offer an custom shaped heavy duty "washer" that fits between the screw and handle that contours to the underside of the handle to prevent scratching it up.
i bought my first acog in '91-92, when there were no picatinny "flat tops" available. handle mount was the only choice. scope sits pretty high offering almost no cheek-weld, but that was never much of an issue to making hits.