Being a southpaw, options are limited and often fleeting when it comes to big/dangerous game rifles and actions. But the Ruger 77 Mk II seems to be holding steady. Ignoring the .375 Ruger for the moment, the dangerous game cartridge that comes to mind is .416 Taylor since it'll fit a normal long action.

But there's the brass & headstamp issue. If I'm understanding things correctly, I could buy some Hornady cylindrical basic mag brass,

http://www.grafs.com/metallic/product/110016

run it into a .416 Taylor sizing die, trim to length, anneal necks, then I'd have un-headstamped brass ready for at least fireforming if not full throttle loads.

Is this correct? Are there any gotchas involved in this sort of thing?

I guess you could do that...but why not just buy .416 Taylor Brass from Jamison?
If you went to unstamped brass...you could get a headstamp kit from Neco. Then, from good sources,
all you would need would be the ".416" stamped,
it passes...the "Taylor" would not be needed...but then again...I'd just buy the correct brass all stamped to begine with.
Best Regards,
Tom

Another option for headstamped brass is Bertram who has started producing 416Taylor ... plus 378Wby, 460Wby, 500Wby, 458Express 3", 500-416Nitro and a host of other new metrics. Brass quality seems to be better than in the past.
Cheers...
Con

If its available that would be fine, but there's a couple of motivators for the DIY approach. One is that a big box of cylindrical belted mag brass in reserve would allow production of any brass needed for boutique/neglected cartridges; not only the Taylor, but also 7mm Weatherby etc. Another possible reason is simply cost.

You might also need to ream or turn the neck's of the cartridges you form ... particularly the smaller calibres. It's a lot of fiddling about if your never going to take the rifle somewhere where headstamped brass is an issue.
Cheers...
Con

Ah, forgot about neck thickness. Thanks.