Try Lil'Gun with cast bullets over 300 gr Dan, it's a great combo. I've driven 350gr Keiths to 1,200 fps, 325gr Keiths to 1,300+, 300 gr LFN to 1,300+. all from my 5.5" Bisley.
But a good general purpose load is 24.0 gr of H110 under a 270 gr Keith. That does 1,100 fps on the nose in my Bisley, or 13.5 gr of Blue Dot for 1,050 fps. Both very accurate and easy to shoot.