http://en.wikipedia.org/wiki/.700_Nitro_Express www.hollandandholland.com This is the largest rifle cartridge in the world available for civilian use. It's the .700 Nitro Express (yes, 70 caliber). It is manufactured by legendary British gunmaker Holland and Holland, who basically coined the term "elephant gun" with their legendary double-rifles. The guns themselves are stunning peices of art and can cost well over $100,000. The .700 is their biggest round yet and is used primarily for large-game hunting: elephant, cape buffalo, etc. It's sheer size and power makes it difficult to fire, and the guns that fire it are very large and heavy, but if you want the baddest elephant gun on the planet this is way to go. The .700NE is the largest available round to civilians, but it is not necessarily the most powerful. The .50BMG round used in big-bore sniper rifles is considerably narrower in diameter, but it is of a longer and more aerodynamic design. The .50BMG actually is probably more powerful in terms of foot-pounds of energy mainly because the huge high-tech sniper rifles that use the round fire it at such a high velocity. An indication of this is that most .50BMG sniper rifles have lethally accurate ranges of over 1500m while a typical big-bore double-rifle has a range a couple times shorter.