the best place where i got everyone of my guns to 20 is at the bathhouse in sanfran
break all objectives
arm and complete the first 2 emps
on the 3rd emp run away and let the hellbot and 2 omnivaults break the emp which will pause it
the 2 omni vaults and the hellbot will keep on spawning when you kill them
rinse and repeat and just keep the last emp paused
super fast gun xp as the hellbots give as much as hulkers also if you go back up to where the 2nd emp was theres an ammo box and the hellbot and omnis will go up there if you stay there
hope this helps i got all my guns to 20 this way youl do like 5 levels an hour easly
