AR-15 isn't high powered. It's not considered suitable for hunting many types of game in many states. 30-06 was introduced in 1906 (the -06 bit) to fix the 30-

AR-15 isn't high powered. It's not considered suitable for hunting many types of game in many states. 30-06 was introduced in 1906 (the -06 bit) to fix the 30-03 (making it a hair shorter and a lighter 150 grain spitzer "pointy" bullet instead of the 220 grain round nose). The result was faster, lighter, and a flatter trajectory at a weight of around 27 grams per cartridge (I don't know the weight of the 30-30, but I think around 30 grams is probably accurate). The 7.62x51 went down a little to 147 grain, but shaved almost a half inch off the length reducing weight to around 24 grams at a somewhat minor expense of velocity, range, and impact strength (very few people could make use of the extra range and power in combat). The first 5.56x45 was all about reducing size. 55 grain bullet was a fraction of the size while the overall length dropped by almost 3/4 of an inch resulting in around an 11.5 gram cartridge (the 62 grain version adds another half gram or so). The effective range dropped dramatically and kinetic energy was cut in half, but once again, very few people can shoot that far in combat and the kinetic energy was deemed sufficient (though that's debated by some soldiers today). Double the ammo for the same weight is a much more important metric for the army. It's a good cartridge for a lot of things, but it's the weakest rifle cartridge the US army has ever used and probably the weakest intermediate cartridge used in any army in the world.