Hi Chet,
What kind of caps were you using? With my White's I had a lot of the same thing happen with it taking two hits with the hammer, I have switched to the Remington #11 caps and for me it has made a huge difference.
I am surprised you are not getting better groups with that 460 grain Bullshop. Can you feel it lightly engage the rifling when you load it? Have you thought about trying Goex? I know you will get it to shoot better.
Art