Because instead of going "Bang" it goes fucking "BAANG". And usually, means it hits harder, even if it screws the barrel with those rounds.

Oh wow, that's pretty awesome, actually- the Mk16 is a pretty sweet weapon, and whilst Merlin's SCAR-H is different, it is it's brother in that weapons family. I'd love to shoot some guns one day if I ever visit 'Merica.