Always late to the dance, I stumbled onto a Bar-Sto .400 barrel just this past summer. The barrel had been fitted for a W. German 220, which has a wider locking block insert than that on my 220R, so both were sent up to Bar-Sto for a refit.
Back in the .400’s heyday, most folks preferred lighter (< 165gr.) 40/10mm bullets, as they were supposedly more accurate than the heavier bullets/rounds.
Those factory .400 Cor-Bon rounds you picked up are quite warm! Personally, and this isn’t based upon anything other than the fact that I don’t want to beat up the 220R’s alloy frame, I reload my .400 Cor-Bon (135 & 150gr. Nosler) somewhat softer than those factory offerings. Not too surprising, the 220R is every bit as accurate with .400 Cor-Bons as it is with .45ACPs. Oh yea, I did pick up a bullet cannelure tool to offset possible bullet set-back issues & I like run a Wolff 22# spring with the .400s.
I look forward to reading about your experiences with the .400 Cor-Bon!