BCB,
I think 3" @ 100 for .357 mag out of a lever gun isn't that bad, really.
I always want to get sub-moa out of every thing, but for that bench rest accuracy, that's pretty much bolt action territory.
Have you read Veral's book? I never knew there were so many possible details that would effect your firearm's accuracy with cast or jacketed bullets.
The first line of attack seems to be fire lapping to cut those groups down, but he says with nothing you do will fix a bad out of ballance bullet from a bad or marginal mold, size, casting proceedure, on and on.
...and he says quote,"I've found that after a little lapping, and with a good bullet design, you can do nothing wrong with lead in a Micro Groove barrel!"
Mine would not shoot off the shelf cartidges worth a damn, ever, but when I went to lead, groups immeadiately shrunk.