.54 cal powder load?

[B-Davis]

So, I just purchased a .54 cal rifle (Pennsylvania style made by pedersoli), it has shallow rifling and is 8 lands and grooves. I have a round ball load for it. It looks more like our rifled musket barrels in terms of rifling. It is a 1:65 twist, I have a Lee .54 cal minie that is 415 grain, front heavy. Anybody have suggestions for a decent powder load? Just trying to figure out a decent starting point.

[Muley Gil]

I would start at 40 grains of FFFg and go up, to see if the groups tighten.