Hello Brent.
Have you thought about having a mold cut with a wide forward driving band similar to what TC does with their maxi bullet? I would think that a .150 band .003-.005 over bore would be easy enough to start but would keep it down there regardless. That in conjunction with a well lubed bullet should be ok.
One other option comes from the folks who shoot slug rifles. Some of the molds I have seen have a bullet base rebated for a cloth patch. As strange as it looks, they seem to shoot very well, although patches would be another thing to carry along.
BTW, where did you get the info on Pedersoli's 12 bore and twist info? I have another post regarding this.
Still curious about that.
Good shooting
Tom
