So basically you're having problems because you're doing everything wrong...
Bullet too hard...bullet too small in diameter...wrong powder...
You have several issues going on all at the same time and it might be confusing to try to figure it out.
I'd start over...
A softer .454 diameter bullet 250 gr bullet would be a good place to start.
I prefer coated bullets.
I like Bayou Bullets. They will supply that bullet with their bullet-proof coating in a custom diameter at no extra charge at a good price....you just have to ask them.
They are good folks. Their bullets are probably harder than necessary, but their coating is so good that I would challenge them to lead with any load. Plus, they cost a lot less.
Titegroup powder is known to be problematic in some circumstances, and I don't use it for a number of reasons. A powder like Unique is more cast bullet friendly in the Colt.
The good news is by starting over there's nowhere to go but up...
