Best pellets or slugs for a flashpup

I have the flash carbine in .22 w hawke airmax 4-12x40 and ive found mine likes the jsb 18.13's and the h&n barracudas the best. Itll almost put the 18's pellet on pellet at 50 yards for spurts and a little over 3/4 in groups out close to 75 (73 to be exact). I took an english sparrow the other day at that distance (73) and was just giddy! No slugs yet but w the accuracy im getting im gonna stick with the jsbs.