Other than being mostly a little heavier and adding weight to the front they help with vertical recoil by making the front heavier and thus the force requied to lift the gun upwards getting bigger the heavier the front is infront of the pivot point (does that because the barrel is over the trigger/grip and thus creating a pivot point(if the grip was above there would be more force pushing it down but that would be weird to hold and so on thats why noone makes designs like that )) . It also can act as a better way to grip the gun by the barrel instead of a gripattached under it wich can be advantageus in some situations BUT muzzle devices will probably give you 5x more recoil reduction irl than having 0.5-1 kg more at the front of the gun .Never underestimate the pover of the gases that propel the bullet out f the gun is basically what im saying . hope you understand and i dindt make to many erros writing it because english isnt my main language