guns

I think of it as the "Uzi-style layout" (although technically the Czechoslovaks were actually ahead on that one with the Sa 23-26, and there's handful of even earlier prototypes, like the MCEM-2 and Shpitalniy, and of course the Japanese Nambu Type 1, which actually did enter production albeit in small numbers), or to be more verbose - the "magazine-in-pistol-grip layout". But there isn't really a proper term for it AFAIK.

The problem with trying to scale this up to a rifle cartridge is that the magazine-grip becomes too large to really grip comfortably - the Soviets actually did try this:

It could work if you do a sniper-style grip with the thumb resting on the side: https://www.snipershide.com/precision-rifle/wp-content/uploads/2020/03/0882165534b80b3f2734738d0b7a2.jpg (linking this directly since I managed to hit a rate-limit somehow )

But those only work out on sniper rifles since you're usually shooting from a very stable rest, and your trigger hand isn't actually doing that much to hold the gun in place - the bipod or whatever else you're resting the gun on the front, and a monopod on the stock or your other hand at the rear do that, while the shooting hand is mainly there to adjust aim and operate the bolt. On an assault rifle though, that hand does a lot more, and with a janky grip like that the weapon likely wouldn't be as controllable.

No, it's chambered in 5.45x39mm, the same caliber as the AK-74