on first 3 maps its quite possible to achieve 2147+ rounds and der riese i dunno >.> depends how good u are . but this can only be done in solo (unless u wanna play for a month straight with more players lol..)
43 solo and 24 with 4 or 3 people.
its kinda hard, not only due to more zombies, but the others always want to camp at the mystery box, even if they have an MG or Browning. i just buy a thompson and i dont think i throw that away.