"Using Hornady factory ammo we have measured the velocity to 730 m/sec "

mm, by my calculations, that would be 2395 fps. Please correct me if I mis calculated.

Hornady claims 2225 fps for their 300 grain .405 ammo. My chronograph tests show Hornady Factory 300 grain ammo at 2225 to 2250 fps. I keep my 300 grain hand loads in that range so as to shoot to the same point of aim as factory Hornady. My .405 double was regulated with Hornady factory 300 grain ammo.

In all my load research, 2400 fps for 300 grain .405 bullets is as fast as has been loaded and reported.