I traded for a nice 40 cal barrel and have been thinking about a .400 Whelan Imp. with 40 deg shoulder(.458"dia) made on 30-06 cases fire formed to expand shoulder area for better headspacing anchor.
I have a 1908 Mauser large ring action I'm thinking about fitting it to.
The barrel is chambered in 40-65 at present with .410" groove .400" bore as near as I could check with a
.398 slug swaged to fill grooves. Twist is 1:16".
Has anyone any experience with the .400 Whelan Improved ?