I don't think its your load but you failed to mention bullet weight. .452 dia work well in all my .45's, USFA and Colts with no leading. You might want to check chamber throat dia., it's best to match bullet dia. to throat dia. You should be able to push your bullet through the chamber throat. You might also try a softer cast lead bullet.
I suspect your forcing cones might be a hair rough causing the leading. Purchase a Lewis Lead removal tool from Brownells. it comes with a forcing cone cleaning attachment that will help polish the cone. I used this tool on each of my pistols the first 3 to 4 times I shot them. I did get a little lead out of one Rodeo the 1st couple of cleanings then it quit. I'll use Lewis Lead remover now once a year without getting any lead, roughly 5,000 rounds per pistol. I use JB Bore paste with the Lewis Lead remover.
WH