bigleague...
for a brief synopsis... 7mm is the diameter of the bullet... there are many different cartridges that are 7mm. The 7mm Mauser (7x57) is a good old cartridge, a spectacular deer cartridge. The 7-08 is a short version of the 7x57, ballistically identical, but will work in short actions. The 280 Remington is basically a 7mm-06..or a 30-06 that has been necked down to 7mm... more powerful than the 7x57. The 7mm Remington Magnum is probably the best known 7... it is a belted cartridge, and is somewhat more powerful than the 30-06. The 7mm Ultra Mag is bigger and more powerful still, and is better suited to long range deer and elk hunting. There are others, but this will give you a brief idea of some of the choices. None of these are interchangeable....