I've had them both and there is a 200fps+ change, difference between them at the muzzle - sometimes a billte more, sometimes a little less- all dependent on the barrel, it's length and idiosyncracies.
; 2,600fps for the Whelen and 2,800fps for the NMag.
; I'd go the Ackley Imp .35 Whelen and get an honest 2,650fps to 2,700fps with 250's, but would rather see a custom 300gr. at about 2,400fps.
; I don't think African rounds need to be above 2,500fps, nor do I think anything higher tht that is ever required. Yhis is a personal opinion, nothing more.
; The .35 Whelen Improved pretty much duplicates modern loads in the 9.3x62 - as the case capacities are almost identical. Take a .35 Whelen IMP and neck it up to take .366" bullets and you have a round generally ready for fireforming. Same goes for .375/06IMP, neck down to .366" and load and fireform. Of course, the larger the bore, the greater the expansion ratio, the slightly faster powders are used and generally higher velocties for the same weight bullets, but lower SD's of those bullets.
; The main reason for the straighter sided case, is easier extraction when pressures rise with heat. It also allows normal velocities at lower pressures, ie: 2,400fps with 300gr. bullets with perhaps 55,000psi - some 8,000psi below max. I don't know of any 300gr. RN's, but probably Woodleigh, or some other maker. I'd be happy with a 250gr. "TSX", I think.