I talked to a ladytoday atGM about the.54 GM barrel measurements.She told me that the bore is between .540-.542" and the groove is between .560-.564".They recommend patches between .015-.018".Also a .535 ball for hunting.Do you have to double the patch dia. and add it to the ball size?Seems a little tight to me but I'm still learning.I have a .530 mold so I'm hoping it's not usless.A buddy gave me 50 or so .535 balls to try.I can't fathom getting a .020 patch down the pipe.Any ideas what to order or loads for this barrel.Our local gun store has squat for BP stuff so I'm mailorder only.............Got a wack of snow today so I'm not sure if it's worth going bear hunting today as planned? Thanx Harold