I had some of their powerbelt bullets in .54, and all they had was a plastic cap at the powder end, but were lead from the belt to the HP. Do your bullets have a copper jacket, or are they just lead and plastic. If it's lead and plastic, you are good to go.

I use the Hornady Great Plains bullets ahead of 110g of 777 in both of my .54's, and they work every time. The groups I get at 75 yards off the bench are usually in the 1.5" range, which is all you need.