Wendy,its not unusual for a person to make a bold,confident,authoritative post,presenting it as fact....when he is just wrong.It happens often.
Don't get buffalo'd. Just laugh
I've never had a leading problem with my Ruger Super Blackhawk 44 Magnum shooting full power loads in excess of 1300 fps.I even cut the gas check feature out of my mold and abandoned gas checks.I cast wheel weight. That same load is higher vel out of a rifle and it works fine.
Folks load cast bullets with gas checks in rifles up to near 2000 fps with success.
Alloy matters,lube matters,bullet fit matters.To load the gun,the bullets have to fit the throat. Use the largest ones that slip into your throats.
Maybe,in some cases,bullets of moderate hardness will "bump up" a bit as the pressure hits them.Harder bulletsare not always better.
Undersized bullets can allow hot gas to by pass them,and that will cause leading. Even at 800 fps.
Mr Bob Wright seems to know his way around 6 guns. I'd listen to him.Apparently your gun shoots pretty good.
Enjoy!
I do agree that bullets,at minimum,should be bore dia,and +.001 or .0015 is preferred.Seems like you know that.
I do have history as a machinist,and how you measured your cylinders matters.If you are using calipers to check an ID...well,your throats may be better than you measured them. If I was using trusted,tested,calibrated dial calipers on a .451 ID,even with "touch" I can't claim I can measure to .001.
MAYBE .002,...but not to qualify a part.
I'd prefer pin gauges or a plug gauge. You might try a new,not pulled,jacketed .451 bullet and measure it with a good micrometer first.Its a "make do",but I trust it before calipers.