ammo, right in your own home. Suspend a tarp to catch the wax bullets, the primer wont give the slugs enough power to pierce a canvass tarp. You can be learning how long it takes you to react to a signal, and just hit with an "aimed in" gun, to react, raise a lowered gun and hit, to react, traverse across an area and hit, to draw and hit, etc. That information is priceless, worth far more than just some more rds launched at the range, either group shooting or plinking. Finding it out can be a lot of fun, too. Just keep a notebook, so you dont have to try to remember everything, when it's time to evaluate whether or not such and such a response is tactically sound.