Mine loves the “22 Kings” 25.39 grain JSB’s. I have run them from 670 to 870 FPS and they are vary accurate at any speed. 
The Crosman HP’s do very well at 950 FPS.

The JSB 18 grain and 34 grain shoot terrible.

Bobs boatail slugs are not good in it at all.

I have cleaned it, but only once

The barrel is 20 inches and on a Huma regulated Skyhawk.

Hope this helps and stay safe,

Roachcreek