Ummmmm, long story...

7mm is the diameter of the bore or .284."

Now there are several cartridges based on that "caliber" (7mm).

Each of these cartridges has its own characteristics for case design, length, etc, etc, etc.

The "cartridges" came about mainly because someone felt they could do better than another cartridge of the same caliber for some reason or another.

Now with that said, here is a partial list of some the the more popular 7mm cartridges.

I think the 7mm you are reffering to is the 7mm Remington Magnum, introduced by Remington can't remember when.

The 7mm STW (shooting times western) was a wildcat that was developed to increase the potential of the 7mm bullet.

Among other 7mm cartridges are the 7mm Mauser (7x57), the 7mm-08, 7-30 Waters, 7mm Weatherby, 7mm WSM, and the 7mm RUM (Remington Ultra Mag). I left out a lot of factory cartridges also available, as well as many wildcats that are out there. These are some of the more popular ones. Each was designed to do one thing that someone wanted it to do.

A good website that has info on the cartridges, both wildcat and factory is www.reloadbench.com

It has good info on the many cartridges that are out there. Just click on the info for wildcat and factory rifle cartridges and read more info. HAVE FUN!!!