Okay. Weatherby's 378 came out in 1953 and 460 in 1957. 458 Win in 1956 and 416 Rem 1989. Not sure I see a significant connection. Kynoch didn't fold up till 1970 and 458 Lott made its appearance the following year. Perhaps a connection there? Not sure who was loading Lott ammo. 458 Win was almost an instant flop due to poor powder in their factory loads initially. Their cartridges didn't agree with African climate. Some say 458 Win has never recovered from that bad start. According to my PH and lodge operator, for whatever reason the 416 Rem has never been popular in Africa. Perhaps this has more to do with rifle design than cartridge?
So Weatherby had the jump on its American made DGR competition ... but never was competitive. It seems the demise of Kynoch, the classic Africa cartridge maker, wasn't a factor. I suspect rifle design probably was the factor that most hurt Weatherby's chances of breaking into the classic African gun market. Clearly, if you want to break in with a new rifle design AND a new cartridge, you better have it ALL together.