Theres like 2 barrior glitches i know and I do the gun glitch
i dont really bother with barrior ones, all i do is
open all doors apart from the 1 in mp40 area, have 1 guy camp on window the other site next to the electric barrier switch, on balcony, all zombies come in one nice straight line, PTRS is best for this till round 22, then raygun/browning/mg42 u no how it works, by like round 30 theres like 0 zombies all stuck outside