Is your 450/400 Hollis an A.Hollis or a I.Hollis? There are at least 2 A Hollis 500/450's here.

BwanaNelson has been doing some work for Zoli in the 450/400's they're building now. And IIRC he said that if the Hornady factory load bullet is pulled and 1 grain of powder removed it'll regulate much better. Maybe he'll add more.