I loaded my 45-70 double with a 400gr speer to 1850fps with 55grs varget, and according to hodgon it should develop around 25000psi.

I chronoed it and with 26" barrel they where around 1851fps.

If i bought a baikal double in 45-70, thats what i would use. I dont think it would be to much as they are using 30-06 in the same gun, but i would switch to wodleight 405grs instead. Even if they are a bit hard and would probably dont open to well at longer ranges(+100m), they are still as big as a fully expanded small caliber bullet and would give great penetration. And teoretically a 300gr bullet at the same load should shoot to regulation, but i never got to test it, and why should one use a large caliber with a light bullet? its easyer to use a smaller caliber instead isnt it?