So.. I played a lot on esl MW1/MW2/MW3 and black ops. I am playing for few days SnD in ironsight and my conlusion is...
If you are good in quickscoping - go for blaster/dsr1
If not - there are two ways - ar57 / mp7 (ar57 will be probably nerfed because it is so overpowered now...) - smg is my vote - soft bullet, silencer and precision barrel.
If AR then you can stay with ak12 or go for scarh/ak47/tar21. - same like smg.
Belive me.. Silencer is "godlike" on SnD, but you can replace it with scope if you can't play without it. Precision barrel is must have. Much less damage drop with distance... But why SMGs? There are only small maps. ROF of smg are overhelming all rifles except famas.
Oh. I forgot about FAMAS
It is also a good choice couse of huge rate of fire and low recoil 
About h417 - it's kinda strange weapon. You can easly kill snipers, but non chance with smg and it is quite hard with fast AR but if you can spam mouse button - it is still quite good weapon in close quaters.