I have an Optima Pro as well (mine is a 50cal). Bought it at the end of deer season last year and I've just begun shooting it. To make life a little easier on myself I've decided to shoot 150 grains of pyrodex pellets in my gun (maximum power and easy to find the pellets in about any sporting good store). So I've been experimenting with bullets and primers. So far I've tried Powerbelt bullets in 270gr and 245gr (both aero tips). With those bullets, I've tried the Remington BP primers and the regular Winchester 209 shotshell primer. So far I'm averaging under 3" groups at 100yards. Next I'll be trying the 223gr hollow-point bullet.
All of these bullets have the potential to perform at 300 yards. Powerbelt publishes their ballistics chart on their web site at: Powerbelt Bullets
According everything I read about modern muzzleloaders, bullets (non-saboted), powder and primers says that you can shoot 6+ rounds between cleanings. My experience shows that accuracy serious deteriorates after the 3rd shot.