One of the issues IRV touched on, but many may not entirely understand, is that a .50 BMG RIFLE, has a dual impulse recoil. This effect is caused by the muzzle brake. In our testing back in the early 90's, we found up to a 21 g reversal in the recoil as the cycle was completed. In other words, after the rearword movement of the rifle, it was jerked forward a very short distance by the effect of the muzzle brake. This is why in in early days (late 80's early 90's), so many scopes would not hold up to use on a .50. I cannot tell you how many scopes I saw destroyed by the .50 at matches. At that time, the only scope that was reliable (for the most part), were the OLD Leupold Mark 4 series fixed power scopes that were originally made for the Navy. The one I still have is marked on the bottom of the turret saddle, "Leupold Mark 4 Ultra 20X 1985" They used an etched glass reticle and had a 40mm objective. By todays standard, it it quite dark looking through it! LOL!. It wasn't until Nightforce came out with their Competition series scopes that we had an alternative that didn't come apart. This was in large part because Jeff Huber listened to our needs. He used to come to the matches with a bunch of scopes, and ended up selling many at the matches. He did the same thing for the military after I showed the very first NXS scope to the Navy late 1998 I believe. Piston type air rifles or pellet guns have the same problem, which is why they sell scopes specifically for piston air rifles. The piston slamming home drive the rifle forward. Most scopes were made to resisted the normal recoil to the rear. It was this forward and back that caused the scope components to come loose. As far as most nightvision clip on devices, they are all rated up to .50 BMG. They have more robust intensifier tubes and are mounted in such a way as to reduce the effect of the recoil. I do not think all thermal vision device have quite caught up, but I a may be wrong with military issue items. So in image intensification and thermal devices, they must be constructed so that both the optical components, and imaging tubes must be rated and constructed with these issues in mind when it comes to .50 rifles. The M107 is probably the softest recoiling .50 rifle out there due to is recoil operated semi-auto mechanism. A standard bolt action rifle is significantly tougher on an optic.
Scott