I built two .400 Whelen rifles on M98 actions about 30 years ago. The myth about the .400 Whelen surpasses its utility. My plan was a large caliber cast bullet rifle using commonly available .30-06 brass. Making cartridges was not too difficult. Feeding issues from the too short M98 magazine well made for short or deeply seated bullets. The minimal shoulder caused headspace issues with anything less than full power/pressure reloads. To put it mildly, it was a great idea, it just didn't work out all that well. Now, .400 Whelen Ackley Improved on a .30-06 action like the M1917 or an 03-A3 was an entirely different matter. The M98 action is best with 8X57 length cartridges IMHO.