A new optic is launched by Trijicon specifically aimed for use of machine guns, the Machine Gunners Reflex Sight (MGRS). It has two interchangeable knobs for the M2 and the M240 machine guns so the gunner can dial in target distances and it is claimed that it increases the probability of first round hits.
Looks like it is something for airsoft players to wait for a replica version. Press release below:
