First off welcome to the forum CRDNLPLT. Stan has some valid advice but buying several brands & weights of ammo can get costly. Unfortunately I do not have any experience with a Rossi in this caliber so I could not give you a clue as to where to even begin. However, I can offer a suggestion. If you do your shooting at a gun club or public range be sure to go on a Saturday or whatever is their busiest day when there are better odds of others shooting .243s there and ask fellow shooters if they would be willing to trade a hand full of whatever ammo you brought for a handful of theirs. Good luck and don't forget to give us a range report.