I'm regulating barrels on a Pedersoli Kodiak .58 cal. The barrels are 24 inch and have 8 thou deep rifling in 1:48in twist. My favourite projectile for it is a patched round ball.

I managed to find a copy of the "Building a Double Rifle on Shotgun Actions", but it'll still be few weeks before it arrives. I also found a thread where someone mentioned locating the muzzles 40 thou nearer than breeches (center on center) is a good starting point. Originally as set by the manufacturer the muzzles were 160 thou (4mm). This was way too close. Also the barrels were bent, but this is a separate thing I'm resolving.

Does anyone with experience of regulating DRs have a suggestion what would be a good starting point?