Nice!
Damn, I forgot that AKMSU is 7.62. But anyway, I think a 5.45 AK is better with that short size and on short distances.
Hmm, I actually just think about to have both weapons ingame.
What about to let the AKMSU as it is now, with only a drum as attachment?
And have the AKS74U without the drum, but silencer (suppressor, what ever), and the nadelauncher, maybe a sightning system like a small scope would be good.
This weapon should just have a little diferent skin, like I explained, darker metal (black?) and red/brown grip as on the pics I posted.
It wouldn´t be any harder work, cuz the model is like it is, maybe just the magazine little slim. The animations would be the same. For the nadelauncher you could use the M203 animation. You have only to make new reload animations (and the nadelauncher bullet mag reload).
http://world.guns.ru/assault/aks74u-ts.jpg