For those considering modification to larger cartridges, you might want to slug the barrel of these guns (talking more Pedersoli here) first. I had a customer send recovered bullets and slugs from his and they measured .4556". Euro 45-70s seem to tend small; down to the minimum SAAMI spec. That's fine for a low pressure 45-70 and soft/thin jacketed bullets but I would think twice before trying .457-.458 steel jacketed or mono solids in them. The owner had "gotten away with" steel jacketed solids but I wouldn't recommend it.