Levallois, Is this a double rifle? If so, then a regulating starting load with smokeless powder will be with the 270 gr bullet, and 40 % of the Black powder load, of 120 grs, or 48.o grs of IMR 4198, with the airspace taken up by Dacron fiber fill, to hold the powder down against the primer. The dacron fiberfill can be found in any fabric store, it is pillow stuffing. Enough should be used so that the fill is slightly compressed when the bullet is seated. To quote Ross Siefried on the use of dacron, and 4198, for regulateing a black powder double rifle with smokeless powder! Quote: We must find something better because, with this recipe, we only get perfect velocity, perfect pressure, perfect accuracy,and perfect regulation. Un-quote