Well, for a .357 like your example, best results would be with a cast bullet using a good BP lube, like SPG, and then it's a matter of using enough BP to ensure you compress it a bit (like 1/8" compression) when seating the bullet. Not an uncommon thing amongst cowboy shooters; .357 with BP works pretty well for that. When you get right down to it, a Ruger Vaquero is designed as a smokeless gun, too...but my .44-40s didn't even see a round of smokeless for the first year+ that I used 'em.
