Well you clearly don't know a lot how fire arms work.
You see,the stock I is to short,because the shooter need some space between hes arm and hes hand for better aim.
Second,like Deltayo said,this gun can't clearly be an Small Machine Gun (SMG)because no SMG is using a 7.62x54mm/7.63x51 bullets.
This gun can maybe be a compact assault rifle.
I can see that your sketch of a gun includes a built-in/integrated suppressor.
While this is in some cases,like the MP5SD3,this is true,just be sure you make the "fire" sound a suppressed one.
The MP5SD3