As I recall, Willis' character is hired to do a "brutal assassination". This goes a bit over the top, obviously.

Willis was going to kill him anyway. He was this assassin that nobody could track down, and Black had seen his face.

Also, Jack Black's character kept asking for more money to complete the project. This was basically an assassin's way of firing the IT department.

Looks like a M2, oldest weapon in the arsenal, with a Canon DSLR w/ 600 mm L lens on top. Supposedly using depleted uranium discarding sabot ammo, but the real ones use tungsten. Overkill against a soft target like Jack Black.

It would work fine, except the alignment between DSLR scope and weapon would get jarred pretty easily in that mount.

Yeah, I thought it was supposed to be some kind of sniper weapon, but it seems useless for that. And it also seems useless as a machine gun.

I gather Willis' character is supposed to be some kind of assassin? This doesn't seem like a professional practical weapon to me. This looks more like the gun equivalent of a monster truck.

I don't plan on wasting my time on this film but this sort of thing would be useful for a small team ambush of a lightly armored target. Find a straightaway the entourage will take, have this thing at one end shoot out the engine blocks, hire some cut rate rooftop snipers to pop anyone that stands up.

Militarily, remote mounts like this make huge sense for static defenses with big signatures, like heavy MGs, AT/AA missiles, etc. Have one guy for every three, somewhere in a cave or behind the hill, and networked defensive weapons could shut down an advance with practically no casualties. Artillery barrage knocks out mount 1's wires, just switch channels (and run a new line to 1 at night).

If I recall the movie correctly, the thing was mounted in a parked minivan within range of the sniper's target and then operated remotely.