The bullet IS labeled as to which BORE it fits. .308 fits a .308 bore. 7mm or .284 fits same.
There is a range of bullets for any given caliber. .308 runs from approx. 100 gr to up to 240 grs with plenty in between.
As for names of chamberings that can get crazy. Some are based on their bore and length like a 7 x 57. Some are named by their date of use. 30-06 is 30 cal which began use in 1906.
Some are proprietary like the 300 WSM
(Winchester short magnum).
Still say looking at a few reloading books will clean much of this up.