Pretty much all guns listed as 7mm in any part of their name throw a bullet of .284 diameter. The rest is individual to each cartridge re: case size and powder capacity.
I assume you meant the difference between 7mm/08 and 7mm Rem Mag. The bullet diameter is the same----- the powder capacity of the case is WAY different. Basic difference between the 7mm Rem Mag and the 7mm/08 is about 15 grains of powder!
Other 7mm cartridges include, but are not limited to....
280 Remington/7mm Express Remington (same)
.284 Winchester
7-30 Waters
7 x 57 Mauser
7 x 61 Sharpe & Hart
7mm Weatherby Mag
7mm TCU
7mm/06
7mm Mashburn Mag
7mm STW
7 x 64 Brenneke
7 x 72R
I'm think all above are of .284 diameter--------- but I'm not positive about all of 'em.
There are more,--- but most of the others are pretty obsolete, rare, or just plain impossible to obtain or create.
Stubblejumper set you straight on the usefulness of the 2 cartridges.