The chamber is to small on that setup. Will have to run a high reg pressure to make up for it.
I have a 25 with a larger chamber and reg is set at 1800 psi. With 25 heavies I can turn up the power wheel and get them in the 920's. I usually shoot them in the 870-880 fps area.
I also have a .30 cal with the same bottle and a over size chamber. It shoots the 45 gr in the 880's with reg set at 1350 psi for over 100 shots.