This is much easier with two players. On the zombie map Kino Der Toten, open the doors which lead you outside and purchase and AK47u. Both players must do this.

When the dogs come for you each player get into an individual corner fairly close to each other.

One player shoots one dog and reloads, then the second player shoots the next dog and reloads.

Keep switching between players and constantly reload and by the time your done the dogs will not have touched you and you can get the max ammo.

Bear in mind the AK's have low ammo capacities but are really powerful.

Don't buy an MPL, they are cheap but weak.