Have you tried Exact Express, the 7.9 grainers? They are the pellet of choice in most of my rifles.
The odd one out is the Daystate Airwolf and that really goes well with the JSB Exact heavy. They come in at 10.34 grains, mind, about the same weight as the Bisley Magnum, and their flight path drops off rather faster at longer ranges.
Not liking Exacts sounds like the rifle prefers a harder lead. Crosman Prems are pretty hard. Try here for good prices: