I thought 338 Lapua. I already see a couple possible weaknesses.... Camera and gear drive mechanism. But they may have armor off for display, and secondary sighting/camera devices...But, with proper operator and considering the range of caliber ? in tandem with other technology ? This is one bad SOB...I wouldn't wanna be on the receiving end of it...
The weight alone makes for some major possibilities. But I still see the sighting as a weak point. As the Russians found out in tanks, at where ever it was....They threw tarps over the tanks, fire bombed the tank, and cooked them in tank, or shot them when they came out. Brilliant really.