All Soviet guns were real trust me bro
Just looking at one of them, T20 with E variants were a reality and lost steam when Japan surrendered. This was the daddy of the M14.
Others you listed were reality … but no matter what I say, it will not be good enough 
The whole game is not reality but I think the devs have did a good job at a WW2 game for fun.
I stick with mainly BR2 and BR3 to give it a more “original” feel