The manual says to use various types of ammo, to find what your rifle "likes" and be SURE to read the recommended and NOT ammo types. Also be SURE to clean/lube it BEFORE firing, to remove all the packing grease and gunk in the gun. You cant go wrong with Federal bulk packs. Other than that just be sure to stagger the ammo properly to ensure proper feeding, and have fun. The "break in" will take care of itself. I have about 6k rounds in my 15 22 most of it are Federal bulk packs, Id say at "least" 4k+ of the 6 at minimum. The rest of it is mostly CCI and a few others I had lying around when I bought the rifle. Lastly, and not least.. welcome aboard! Its a GREAT rifle, hope you get in lots of trigger time for the first few times you get to fire it at your local range.