You'll want to try several different projectiles/sabot/powder combinations to find what that barrel likes best.
Finding and working up a load will be pricey, but once you find it, you'll be happy and can stack deep at a reasonable price.
I've tried everything in my CVA's... A whole slew of sabots and bullets (in 44 and 45 cal), PowerBelts from 245-295gr and up, pyrodex and 777, loose and pellets.
Some of my loads changed over the years... and I actually settled for fractionally larger groups for better terminal performance... A tighter group on paper is meaningless in the field if it doesn't penetrate or expand reliably.
My old Optima Pro absolutely loved the 295 HP Powerbelts over 3 Pyrodex pellets... 100 yard Cloverleafs. Kicked a bit, but hit where I wanted, expanded AND penetrated deep enough to ensure whatever was under the crosshairs was DRT.
My newer Optima V2 shoots almost the same POI at 100 yards with 295gr HP Powerbelts and 300gr 44 cal XTPs in smooth green Harvester Sabots (Both with 100gr loose 777, 1" poi difference at 100).... It cloverleafs the XTPs, groups the PBs about 1.75-2".
The PBs group widens considerably past 100.... the XTPs shoot much tighter and more predictably past 100 (due to higher BC).
I'm (finally) about to make the switch to Blackhorn... been sitting on a can and the replacement QRP plug for almost 2 years waiting to shoot up my remaining 777.
I've heard nothing but good things about it (besides the price) and look forward to a decent weather Saturday sometime soon to start working it up.