Brian,
Better to post this question on the accuratereloading.com double rifle forum.
Reckon it's hard to give Hornady a call from your aor... Can't imagine that the Hornady pressure is more than what the old British rules list at 16 tons/sq.in.
I've seen two pressures listed for the .405 Winchester, one at 44,000 CUP; the other this from Chuckhawks: "Current SAAMI specs call for a maximum mean pressure of 34,000 psi for the .405 Winchester."
Bottom line would likely be (subject to accurate conversion of tons/sq. in.) that the 450/400 3-inch gives more pressure than the .405 Win maximum...
Regards, Tim
