I would start on the light side with the load, somewhere along the line you indicated the twist rate, which made me think it's for a lighter load. Many of these rifles shot a surprisingly moderate charge, especially if the rifle is built to a lighter weight.

Make sure your lube is not petroleum based, it will turn the fouling to an asphaltum-like state if it is.

Try to get some Olde Eynsford powder if you can.