You want the big picture... Long ago, 1800s, Paul Mauser designed the rimless case with a rim of .473 inches (in metric, of course). 8mm x 57mm is probably the earliest and most famous. [6.5 x55 Swede uses a different rim --larger slightly--for reasons I have never seen stated, but since I don't care... All the other Mausers are this same size. 7mm, 7.65 Belgian, etc.] Uncle Sam copied it for the .30/'06... just made case longer. About 75 years later, Uncle Sam continued to use it... studied hard on the .300 Savage as a new military round. Neck was too short, but it (.300 Saveage) was made from the .30/'06 shortened. Same .473 rim diameter. Uncle Sam decided to make the neck longer and the rim a trifle thicker for use in full auto weapons... And the 7.62 x 51 NATO was born. Of course, Winchester called it the .308. And almost as quickly necked it to .243 and .358 ... Later, 7mm and more recently .26 (.260) and now .33 (.338 Federal?)...
So, as said, any rifle for the .308 is pretty ideal for any of these factory rounds. Now if you get ambitious and go .243 Ackley Imp with the longer body and sharper shoulder, then the magazine might need a trifle of work to assure reliable feeding. Maybe not. And if you decide to go shorter, eg. .250 Savage or .22/250, equally, no problem, as a rule. LUCK.
