When selecting optics for your weapon, it is important that you examine the individual platform and decide on the best course of action based on your intended use. This will help you select the right optic for the job at hand. If you use an M240 machine gun in any capacity, the best solution is this EOTech 552.XR308 Holographic Weapon Sight.
Built as a no-nonsense holographic sight, the 552 is the optic of choice for many elite special forces groups and users include government agencies like the ATF, DEA, and FBI. Of course, this configuration was built with the military in mind. The reticle on this model is aimed to serve the M240 machine gun and is matched to work perfectly with that weapon while using .308 150 grain M59 FMJ with a 24.8” barrel. As it is built for military use, this model features a tough exterior and is fully submersible up to 10 meters. Powered by 2 AA batteries, it will provides up to 1,000 hours of continuous use while operating with lithium batteries.
So, if you have an M240 and are looking for the perfect optical solution to compliment your weapon platform, this is definitely the way to go.