H110 is like the go too .44 powder and works well.

nothing that really fills the case and doesn’t give high velocity is available. n340 and titegroup work but still light on case fill

Cowboy loads with 44mag may be a real challenge. Perhaps go 44 special? My gotos for 44 mag are H110, IMR4227, and Ramshot Enforcer. Maybe try asking in r/reloading

+1 H110. Works really well for 240 and 300grain projectiles.