Just finished watching the video. Interesting. My model 76 in .50/95 in smokeless powder, puts the 368gr. FP cast bullet out at 1,650fps and with 80gr. Swiss 1 1/2 BP, at 1,580fps. With 78gr. 3F GOEX, the velocity with the 368gr. is 1,640fps.
I have a new 377gr.DC mould from Accurate Moulds (thanks for the suggestion Mike) but I have not cast any up with it, just yet.
Had to correct the vel. with the 300gr.FP Buffalo Arms bullet, it was 100fps higher for the smokeless load.