I found the Heavy Cannon

[RSSwizard]

The STA-50 which is designed for use by special forces, with a 5 shot magazine. The large barrel shroud is a combination suppressor and muzzle brake. I believe it weighs in the 20 pounds range.

Sure bears a strong resemblance.

[Juku121]

Uh, that is not a man-portable cannon. That's a suppressed, shortened .50 cal. Cannons are generally starting at something like 20mm, at least.

Otherwise, cool find!

[FireStarTracer]

It probably would be closer to this:

Even that would be rough.   There are 20mm anti-material rifles for example but they often require a prone posture and bracing to work.  Even .50mm BMG or other heavy machine gun rounds can have that issue.

the closest IRL would be some sort of man portable automatic grenade launcher - something like this

https://www.thefirearmblog.com/blog/2017/06/21/belarusian-30mm-handheld-full-auto-grenade-launcher/

Spoiler"for huge image":

Only imagine something twice the diameter. Grenade launchers have been made experimentally up to 70mm so its possible...  the line between mortar and grenade launcher overlap a lot.   

Even then its probably something that your biggest strongest guys carry.   Like the gatling gunner in the intro of the first game.