Ok but would your round retain the 13k lbs energy or increase it? 

And would the new gun be lighter than m2

It's safe to say that my round would increase the ME even when just firing saboted m8 API, with the notional big boy rounds specifically for the gun it'd definitely jump probably quite a bit higher.

To an extent though my proposed rounds especially for this gun will hit like a fucking dump truck loaded with cement even before you factor in the explosives in the rounds.

Onto the actual gun itself.

"My gun" is essentially based off this.

Which as you can see was 55 pounds to the Browning's 84. Once you factor in that this gun is dual selectable feed though and my fast googling shows a box of linked brass case 50bmg weighing about 32.5 pounds all up including box, your weapon mount would have about the same if not a little more weight on it if you just went directly with the dover devil herself.

My proposed idea including all the revisions and etc and especially including the lightweight cases links and quick change ammo boxes would actually get you to a net weight savings over an M2 + ammo + ammo box and mount even though you'd have more than 2x as much ammo physically loaded and ready to fire on the gun.

I haven't went through and done all the math on what everything would weigh exactly but even with the new full caliber high pressure rounds in the TV style neckless cases you should be at least weight neutral on a round for round basis.

Where the real savings would come in is on reduced recoil and other forces the mount would have to compensate for and some other things. There you're talking substantial weight and bulk savings!

My goal wasn't so much even to save weight though, weight savings are sorta incidental.

My goal here is to give them something that hits harder, needs less maintenance, is cheaper, is easier to adapt to modern mounts like remote weapons stations while still being able to use it on a tripod with butterfly triggers when needed.

Also some of the things I'd do to the gun design and construction would make for much easier tripod use including not having to sandbag the living shit out of your tripods.

The gun and ammo are only part of the picture. My goal here is to give them something that works better for what they actually do with these gun systems.

It sounds good and a logical improvement.

I still think that weight is inconsequential given that most roles are vehicular. Size of ammo is the real nut to crack.

I even wondered about squared rounds that come packaged in a cube

...you drop the cube into some kind of device that feeds each round to the gun.

And again, an APFSDS with .22 steel projos would in theory allow a round almost as small as 338 but theres the sabot danger.