In my experience, having owned a 416 Rigby built on a ZKK602 (rebored 375 H&H) & shot a friends Ruger #1 in 458 Win, the 416 was much more user friendly. Be that as it is though, after 10 or so rounds from the bench, I was only too happy to let someone else have a go for a bit. It was much more comfortable offhand but you still knew it had gone off. Most of my loads were pretty much full power , in either 400 gr or 350 gr but the sort of loads that Josef is referring to would be not too uncomfortable. 416 Rigby dies come in 7/8x14 threads, Hornady is probably the cheapest for a factory set. Norma brass is good & should be available, might have to wait for the next shipment though, the Speer 350s get some good press on the net, especially at those speeds. Taipan 400grs if still available might do OK at more moderate loadings, I've heard they're too soft for buff but good for practice & would be OK on deer at slower speed, maybe 2100-2200fps.
Steve.