The 7mm is one of the most popular rifle calibers in the world for at least four reasons.
- 7mm bullets are sold in weights (100-grains to 195-grains) suitable for terminating everything from bunnies to bull elephants.
- 7mm cartridges can be fired from "sporter-weight" rifles as light as 6 pounds without crippling the hunters who operate them. I've gone as light as 4 pounds with a 7mm-08 and lived to tell the tale. The caribou and mountain goat did not.
- 7mm bullets can be designed to fly a long, long way while efficiently resisting wind deflection, minimizing drop, and retaining maximum kinetic energy.
- Compared to 30-caliber bullets of the same weight, .284 bullets have appreciably higher Sectional Density for (potentially) deeper penetration.
The 7mms, as most shooters know, use bullets .284 inches in diameter. Mathematically this doesn't make sense because 7mm converts to .2756-inches, which is why the British renamed the 7x57 Mauser the 275 Rigby. The bore diameter in 7mm rifles is considered to be .28-inch, which translates to 7.112mm. Our .284-inch bullets are 7.21 millimeters in diameter, the additional width needed to fill the rifling grooves and seal the bore. The only two 7mm rifle cartridges known to carry the proper label, then, would be the Lazzeroni 7.21 Firebird and 7.21 Tomahawk, two proprietary and obscure 7mm rounds. Such is the state of cartridge/bullet nomenclature. The numbers don't always add up. Nevertheless, the .284-inch diameter bullet is the standard for all 7mm cartridges/rifles.
Actually, there are plenty of obscure 7mms to go around, largely because so many have been concocted. Most are rounded off and labeled as 7mm, some as 28, 280, or 284. Ammo manufacturers in the USA alone build and sell 14 different 7mms. Throw in five produced by Europeans plus several proprietary rounds like the 7mm Dakota and aforementioned Lazzeronis, and we're sorting through an extensive family. And we haven't even mentioned the obsolete 275 H&H Magnum, the 280 Ross, the 7x61mm Sharpe & Hart Super, 7mm Gibbs, and who knows how many wildcats like the 7mm TCU, 7mm JRS, 7mm STE, and Elmer Keith's old 285 OKH.
To serve the greatest number of shooters and readers with the fewest words, we'll primarily cover the extant US-made cartridges, with lighter coverage of the European/British 7mms and proprietary cartridges. If space permits and my typing fingers hold out, I'll throw in a few obsolete rounds and some wildcats. Let's pull the trigger and launch this 7mm compendium!