Try to use Aim Enchance module and use both muzzle breaker and foregrip if it's possible. I also recommend firing short bursts and waiting a little bit that the weapon starts to move down. Everytime you fire, pull the weapon down with the anolog stick you use to aim.
As for weapon skins, some weapons already have in the game (Scar has three skins, Jackal has two skins when you sing-in to gamesas from the game) while others could be received only by buying a specific edition of the game (Hunter, Brawler, Deluxe etc.).