Animations for different weapon styles

I have a set of good animations for use with a basic machine gun style weapon, but I noticed as I equip different types of weapons (pistol type, sniper type, rocket launchers) the arms don't really match the style of the weapon. With some weapons the arms should be lower and more/less outstretched and with some other weapons the opposite would be desirable..

What is the best way to handle multiple animations for different weapon types in a 3rd person camera game? Would I need to make a set of animations for every different weapon type or is there a method to just make different animations for the arms?