I think that instead of a gun glitch they should let you add a third gun once you get to a certain round since you go through so much ammo. The only strategy that I've found to work is playing ring around the rosy by flopper until you max out the zombies allowed on the map and blast them with the zeus cannon. I've only gotten to round 37 but thats the only way I know to have enough ammo to last between monkey rounds without a max ammo or swapping weapons. Maybe once you get to a certain round you could buy another gun slot with all the unused points you accumulate.
