I use .454 balls in my Rogers & Spencer, they seat firmly with a good seal. My powder charge is 24gr of Black Powder (HK fine) I then pack out with a fibre wad or compressable filler such as polenta and seat the balls almost at the front of the chambers. I grease the top with Tallow. I've shot about 300 rounds through it so far without any problems other than the usual cap jams every now and then.

I've got hold of a handy powder measure so that I can reduce the charge a little and find the 'sweetspot' as 24gr is a little too much for the range (although its great fun!!) and I feel around 18gr would give a nice accurate target load.

I've found for maximum 'upset' of your pals on the range you should take advantage of very still misty mornings