Odds are that there will be a lot more paper punching than Bambi shooting.
Once sighted in for targets, it should not take more than a couple of three-shot groups to be re-sighted for Bambi. 20 - 6 = 14, which is way more than enough.
IOW, buy one box of any sort of decent ammo for hunting. For the paper punching, find whatever brand/weight works the best for group size.