My 78 in .177 likes the heavier stuff. It's shoots Crosman Premier Heavies fairly accurately. Same goes for Beeman CroMagnums and a few others.
Not sure on my 79 .22 yet. All I've put through it so far are The Peak pellets, CP's and Beman FTS. It seems to digest them all without any change in accuracy. Just a slight change in POI.