I believe that lead is about 7 or 8 BHN, and that WW's are about 10 or 11 BHN, and hardcast afaik is anything from about 14 BHN and up. When I water drop my WW's they harden to ~24 BHN and I have driven them to 1400 fps without leading. I've driven (oversized .460) 45/70 boolits to ~1700 fps without leading, and they were not hardcast. Air dropped 20/1.
The guy at your pin shoot was just repeating what he's heard before. That's exactly what they used to say (back in the 80's), don't go over 1000 or 1100 fps with lead. We know better now!
What size are your Missouri bullets?