Ricky, to easily get the kills with the hammer, go to road 666, or the strip 2 and on road 666, to to roughly level 30. For the strip 2, it would be much harder but if you can pull it off, get to the 40's. The narrow halls make it easier for all of the zombies to get all nice and compact then when you rush them, they just swarm you. Hope this helps.
Please make the mine challenges 5,000 kills instead of 10,000. It's not like you can exactly rush all of the enemies and get tons of kills with them. I am currently playing on "The Strip 2" because it has such narrow halls which doesn't leave the enemies much space to maneuver around my mines, yet it is still a pain. I don't even want to know how long it must take to get the 10,000 kills with them while on one of the much larger maps. So please at least lower it somewhat. You WILL see better ratings, and better responses to this game. :)