Check any reloading manual, many caliber just mimic another, 7x57 and 7MM08 just to name one...........Duce<><
Absolutely true.
And the beauty of these near duplicates is that many of them were designed to fit into a different action length.
As the AR15 is now the most popular rifle platform in the nation, and as it makes up 50% of all long arm sales, it only makes sense to work toward maximizing its usefulness beyond its original intent. The AR15 was designed to shoot a small light bullet. That little round is not particularly useful for some sporting purposes like taking larger game.
The 30 OSSM is just one of many developments that help make the AR15 more useful for field use. It probably is one of the most useful medium-long range medium weight rounds we can stuff into the very short actions of the AR15.
Clearly we can use an AR10 but that is a longer action, heavier gun, longer gun which all make it less handy in the woods.