almost all cc1, any bullets that are tipped with ridges may give you fitsYou nneed to find smooth tipped bullets), took us 1000 rounds of cci to break ours in, now it loves eley sport and shoots 1/4 groups at 50 yards. wonderful gun. Some mag ramps are too steep and have to by filed down a bit as the push the tip of the bullet up too high 10 rounders especially. They are ammo fussy but be patient find the right ammo and it will soon become your favorite 22 by far. Ours are more accurate than our cz 452's.