Using BP try to keep your loads at 1150 to 1165 fps with a 405 gov bullet. I have used Schuetzen, Swiss, Goex and Goex OE. if you go much past that velocity with a 405 you will spread your groups out considerably. I have shot 535's with 70 gs of Swiss 1.5 in my trapdoor. It is very accurate but I would not do it again as it is hard on the gun and equally hard on the shoulder with that metal buttplate.
I would NOT use smokiless powder in a trapdoor, the pressure SPIKE with smokiless is very different than the pressure CURVE with BP. I know some folks use Trailboss in trapdoors for a low velocity load, however it is a very high pressure powder for the velocity you get from it. I do not know any competent gunsmith that would recommend any smokiless loads to use in an original trapdoor.
wM1