IIRC the 400 H&H is a .411 diameter bullet.....just the same it's never going to be popular if it has to contend with the 416 Remington or even the 416 Taylor. Bullet selection strongly favors the 416 diameters.

From what I've heard of ammo costs the H&H offering will only have a chance of being as popular as the .300 and .375 when it's commercially produced my the majors and chambered in the M-70 and other popular makes.

I'd love a trio of 300, 375 and 400.....but it's just not in the cards now.

I looked at it seriously before building the 404 Jeffy.....
Mybe someday....but not now