Buy as many brands as you can find . . . a box of each is enough.
You should find something to its liking quickly without buying 500 rounds of one brand.
555 and 333 equates to GIGO . . . Garbage In Garbage Out.
I must have an anomaly for a rifle then... my Marlin 795 shoots 555 almost as well as my MkII shoots CCI Blazer. About 3/4" at 50 yards. I only wish my MkII would shoot it that good.