If you have an energy requirment that needs the 400gn bullet at 2100fps then I presume that 3916 is suficient according to this calculater
http://www.handloads.com/calc/quick.asp
If I put in the figures for my 350gn bullet at 2363fps I get 4338ft/lb energy and if I go further and use the ht 90/10 that I ran to 2415fps with 87gn 2209 then the energy figure raises to 4531ft/lb
That makes the 400gn at 2100 fps quite a light load and so getting to the required energy figures with my 350gn bullet would be quite simple.
Hock mould 06610 425 345 to my design on 5-18-08.
I would not hesitate to use this bullet on a buff as the chambered round but might have some of my woodies under it to follow if necessary.