No, it uses the .308. A .50 machine gun like the old M-2 weighs about 100 pounds with the ammo, I think. .50 MG's are mounted, not hand carried.
And yes, the 20mm will pierce a tank, with the right ammo and at close range. It would probably drop a mutie master with one shot.
"Piercing a tank" is a big vague without specifying the model tank you're going to pierce. Modern anti-materiel rifles aren't really anti-tank weapons as much as they're generally anti-everything that isn't loaded with massive armor. Trucks, jeeps, hummers, normal brick walls, and anything else that isn't more or less impervious to normal bullet fire. 20mm, by the way, is borderline cannon ammo, isn't it? It's something like 4 by 1 inch in size and very much something most people wouldn't feel like carrying around only to use on something as fragile as a human.
Using that against a single, humanoid target, be it a super mute or a person, is going to create a movie-style hole through said humanoid (and whatever humanoids may be standing behind). Regardless of how tough they're supposed to be, a single round to the face is going to create immense brain ventilation in a super mute behemoth. Heck, even a .50 cal anti-materiel round should do that, but 20mm? You're just having a laugh if you're killing regular enemies with that kind of rounds.
I wonder what would do more damage, a 5mm mini gun, or a .50 Cal machine gun (I think the M60 is a .50 Cal)
Define "damage". Normal weapons aren't really measured in hitpoints and humans die just as well from being hit with a burst of 5mm (essentially .2 cal) rounds as they do from being hit with .50 rounds. The minigun is going to send so many bullets into a target that it's literally sawed in half (didn't they do this on a tree once in Mythbusters?), while the .50 is simply going to create a number of very large holes in a person. As such, the result in either case is "fatal damage" and there's really no category beyond "fatal", is there?
They do have different strengths, of course. A 5mm gatling would provide much greater rate of fire than a .50 single-barrel heavy machine gun. If the target is light on armor then a greater rate of fire means more projectiles on their way to cause misery. Against armored targets the picture is somewhat different. 5mm is still just pistol caliber and thus won't really go through steel plating no matter how many rounds you're firing. .50 cal is quite a different story as the half-inch diameter provides for a much heavier projectile and thus a lot more energy transfered on impact. Even though the single-barrel machine gun will only be firing at a rate of one fifth the gatling gun, the bigger projectiles will get through plating (or other obstacles) that might render 5mm rounds ineffective. .50 cal would probably also have a bit of a range advantage, but that's just a guess.
Now, what you really want is a .50 gatling gun. Well, you wouldn't want to carry one around (nor would you want to carry the 4000+ rounds it's bound to eat per minute) but I'm sure all that gear would look lovely on Fawkes. :laugh: