I think you should clean the rifle, shoot two groups with what you hope will be your favorite ammo and see if there is any noticeable difference between groups. Then go from there. I realize you're trying to do this on the cheap and not burn up your ammo before you get a good idea of the results.
If you are talking 22 rimfire, you will need to shoot about 10 rounds to season the barrel when you switch brands and shoot 5-shot groups. This kind of testing is very common with 22's.