Yes, agree, I beleive you have experience with 404 Jeff. How would you compare recoil wise. I beleive for a well balanced gun it is less, but is it significantly less?
Loaded within its original velocity "window," the .404 Jeff has significantly less recoil with a 400grn bullet than does the .416 Rigby - and the 416 is typically comes in a heavier gun with a magnum size action.
Original .404J velocity with the 400grn bullet was 2125fps, as manufactured by Kynoch, versus the Rigby's 2350+fps for the 400grn load.
But out of real-world rifles, the 404 ammo was actually doing less than that. Kynoch's catalog velocity, or what today we call the "box-flap" velocity, was chronographed using a
28" factory test barrel. From the 23" or 24" barrels used in the game fields, that 400grn load was in the 1950fps-2000fps range.
Even at that velocity the 400grn load still killed all the Big Critters while imparting a very moderate amount of felt-recoil in standard size rifles. Maybe no worse than a .375 H&H firing typical 300grn ammo.
When Hornady produced its line of .404 400grn ammo (DGX & DGS), they chose to increase velocity to Rigby levels - 2350fps - which was totally unnecessary since that velocity won't kill any better than the original did, but will punish the shooter more.
The only issue with the .404 had nothing to do with
velocity, but with occasional field reports of
poor bullet performance. Today that's a non-issue since modern bullet tech is light-years from the projectiles these cartridges first used in the early 1900s.