Chances are given the beast's size and the speed it is moving towards you that the M249 is a better bet if you want to stay alive and not get bitten. But what about the bullets? Namely the silver on the tip. It is one thing to make six or twelve bullets one Sunday afternoon, but at 200 rounds a minute it's going to take a whole month of bullet making to feed the machine gun.
Worry not you paranormal aficionados! This video shows how to quickly apply silver to the tip of a .223 bullet by means of silver nitrate.
Disclaimer: I haven't tested this myself as I lack a werewolf to try the bullets on. Should you happen to have a werewolf at hand locked up in your basement or one marauding your neighborhood please let us know if it works.
PS, take the revolver with the other silver bullets just in case.