I don't use the Powerbelts and you don't say what type of powder you intend to use. I have a 50 Hawken of Italian origin and use 80gr of Goex FF in it. That is where I get my best accuracy. I would sugest that if you are using BP that you start at 60gr and work up to your most accurate load. derf

FF is aka 2F in BP terminology. You will want to use 4F in the pan.
The real fun begins when you start to introduce other people to the sport. I showed 6 guys how it all works last Friday and after they all had a couple of shots each,4 of them decided to take up the hobby(read addiction) derf

SORRY, forgot to say that this is a flinter.

Sorry that I didn't make myself clear. All I intend to use is B/P. I assume FF would be indicated for a .50 cal. rifle?
I will start with 60 gr. as you stated, and work from there.
Thanks