Why would you want to glitch to 50 when its so easy to do legit? Here's how;
get yourself a sliquifier, monkeys and pretty much any other 2 guns after u get mulekick.
Sit un on the the broken post that leans up toward the an94, shoot the bottom of the post with the sliq and watch the zombies pile up, hit one of the zombies with the sliq and watch them chain reaction die. Whenever u see a bomb or max ammo, toss a monkey and get it then get back up and shoot the bottom.

Rounds will go by just as quick and easy as if u were in a glitch except the difference is u have the satisfaction of knowing u did it legit. Practice timing your sliq shots so as to get the most out of them. But trust me it's EASY! good luck