For what it's worth, here is my experience. I have a 1978 Ruger Blackhawk. It's bore slugged .451, and the cylinder throats were .455-.456. Accuracy was okay, but nothing special. I returned it to Ruger to get a steel grip frame, and while there I ordered a new cylinder. The new cylinder throats slugged .450. I had it opened up to .452, and my accuracy with .452 cast bullets is fantastic. I use a Lyman .452 sizing die, mostly on the 250-grain Lyman 452190 bullet, cast from 1:20 alloy. I used .490 lead rounds balls for slugging, tapping them into the front of the cylinder and then back out with a steel rod.
