I have been thinking about machine gun optics for a while, as I am on the waiting list for a Lage Max 11/15A1 5.56mm upper for my M11A1 (registered and legal) machine pistol. I am fitting the Lage upper with a BlkLbl bipod/handguard, and that leaves the question of what sighting system to put on it. Red dots allow one to maintain a sight picture while firing, but offer no ability to identify targets beyond range of the naked eye. Magnified optics allow much better visibility, but are difficult to use effectively beyond the first shot in a burst. Even a variable at 1x has an eye box and relatively fine reticle.
The solution I have found that I think will be the best compromise is the Spuhr BAM (Ballistic Adjustable Mount). This is a mounting platform that holds an Aimpoint CompM4 red dot and an Aimpoint 3x magnifier and has a BDC allowing both dot and magnifier to be adjusted to hit at 250, 400, 500, or 600m. The Aimpoint has no holdovers in its reticle (which is just a plain dot), so this adjustment allows the dot to be used effectively out to the maximum effective range of the 5.56mm cartridge. The magnifier is fitted via a flip-over/twist-off mount, so it can be flipped out of the way when not in use (ie, after a target is identified), or detached completely when not wanted.
I am really eager to get this mounted on the Lage Max 11/15A1 and actually try it out on the range! This rig is not exactly cheap, and I am grateful to Spuhr for providing me with the BAM mount, and to Optics Planet for providing the Aimpoint and magnifier. Everything Spuhr makes is of excellent quality, and I highly recommend him for all sorts of scope mounts, if you can afford his work.