THANKS .... FYI ... FROM WIKIPEDIA
The .500/465 Nitro Express is a large bore interfere rifle cartridge developed by Holland & Holland and introduced in 1907.
The .500/465 Nitro Express is one of several rounds (including the .470 Nitro Express, .475 Nitro Express, .475 No. 2 Nitro Express and .476 Nitro Express) developed as a replacement for the .500/450 Nitro Express following the British authorities' 1907 ban of military caliber ammunition in India and the Sudan, all with comparable performance.
Holland & Holland created the .500/465 Nitro Express by necking down the .500 Nitro Express 3+1⁄4
The .500/465 Nitro Express is designed for use in single-shot and double rifles.
History of the 500/.465 (3&1/4″) Nitro Express cartridge: The .500/.465 (3&1/4″) Nitro Express was introduced by Holland & Holland of England to answer the demand for a cartridge more powerful then the 375 H&H Magnum (375 Holland & Holland Magnum) . At close to 5,000 foot pounds of energy this cartridge has as much energy at 200 yards as the 375 H&H Magnum has at the muzzle.