Oregon Bill,
I too use the 450 grain .5070 Lee bullet but in a 22 inch barreled .50-45 Rolling Block Carbine.
Results are as you found: "okay" accuracy, but nothing spectacular. I think a big part of this are the very shallow lubrication grooves on this particular bullet.
I'm still playing with the powder loads (smokeless) and the full-loads (blackpowder).
What kind of accuracy can you get?
I've only achieved 3" to 4" groups at 50 yards, which translates to 6" to 8" groups at 100 yards. Nothing to get excited about!
John