223 vs 308 w/o ear protection?

[telomerase]

I think you're right for the wrong reason

The sound of a 223 versus a 308 may have more to do with bullet velocity than anything else. The higher the velocity the more pronounced the "crack" as the bullet breaks the sound barrier.

The shock wave of the bullet propagates away from the nose of the bullet in a cone; I don't see how much of that would hit the shooter. But you're still right about the velocity; the high velocity bullet outruns more high-energy gasses, so more energy is wasted as sound. Thus for instance 7.62 X 39 is quiet compared to .223, yet the SKS bullet has more energy than the AR.

E-muffs are a good idea. (Does anyone know of "e-plugs" that work?)