M60 is beastly but hungry. Flat out better than AK, especially with the skills to reload quickly and on the move.
By the time you're at rank 3 MG skill on Nomad difficulty the T4 M60 I've got is more or less a full auto sniper rifle. Headshots for day. You'll burn through ammo fast (day 14 BM horde went through almost 500 rounds of 7.62, however I kill enough zombies to level 4 times so I'm okay with that, it's about 2 days of mining resources and 2 days of waiting on craft timers in chemistry and workbenches) but you'll burn through zombies just as fast.
My day 14 BM horde 'base' was a 25 block long, 3 block high cobblestone and concrete hallway with openings at the mid-way point for zombies to come in. I could back up to a parkour jump up to the top of it, sprint along the top ledge while healing/reloading and drop down on the opposite end. In that environment it was just lawnmowering heads with it, almost 1 kill per bullet. I also ran back and forth along the ledge spearing down when I had to wait for healing and then near morning when I'd managed to burn through almost all my ammo.
However I can't do that with an AK - too much reloading time; you'll have more than a clips worth of zombies to deal with. The 60 is amazing because ROF, firepower and clip size means you can clear a whole wave and reload before they'll fully into the chute.
I'm creeping up on night 21 and am not sure it'll do as well vs irradiated and other high power zombies but man, it's still the ultimate weapon in game I've found so far.