I tried some Trail Boss in my Ruger Old Army. After reading the artical in the Double Gun Journal that said around 70% volume would equal BP pressures, I started there and worked up. Every shot was a hangfire. Percussion caps don't work to light off smokeless powder. It's a waste of time, don't do it. BTW, I didn't see any excessive pressure signs. Caps looked normal, hammer didn't self cock (like it will with a load of FFFFg) Now that converted centerfire revolver using pistol primers, that would be the way to go.