I based my 1450 fps velocity "guess" on chrono readings from shooting 300 grain Remington .458 semi-jacketed hollow point bullets from my Mustang using MMP orange sabots and 110 grains of RS. The next closest match I have is 300 grain Gold Dots in Harvester short black sabots over 105 grains T7 FFFG. My record shows a five shot average of 1637 fps.

Don't know if my chrono is accurate. But it gives me consistent readings from different range sessions with the same loads. My "base line" is the handloads from my 25-06 which read just at 3200 fps with every chrono I've ever shot them over, including mine.