Judson's right. The H&H was the forerunner of the modern magnums and it won the Queen's Match at Wimbeldon(correct me if I'm wrong here) and changed the tide in target shooting.
But he's also right in that the .300 Win & .308 Norma are much better bets, as is the .300WSM, in terms of performance & efficiency, and far more ammo is available for them.
Another drawback, both of the the .300 and .375 H&H cartridges, is that the gentle tapering case for easy feed, which made them an excellent cartridge for hunting dangerous game with bolt actions, also suffers terribly from stretching, should you reload. People anneal and do other various things to combat this but it really can't be overcome and in the end you have to regularly trim the cases.
If you don't mind this(or don't reload) & you're willing either to fork out for a custom rifle with the necessary magnum action or have a Ruger No.1 chambered for this round then enjoy. No one can deny that the old magnums by H&H, Rigby & Jeffrey have something about them. Personally I'd love to have a bolt action in .416 Rigby. Mmmm.........more rifles, argle, drool. :grin: