Well, you can also load your 30.06 with a 110 grain bullet and it will really scream. It would absolutely detonate a small varmint game like a ground hog, and be a terrible choice if you were going after moose.

And, you can get some real screaming fast loads for 10mm. 135 grains were all the rage 15 years ago in 10mm Auto.

All else equal, lighter bullets will have higher velocity, flatter trajectories and usually deliver a small amount more energy on target. Heavier bullets will deliver more momentum and penetrate deeper. Which you need depends on what you want the projectile to accomplish when it hits the target.

Going back to the ground hog and moose comparison: The 110 grain bullet which is devastating to a ground hog would only create a flesh wound on the moose. And the 180 grain bullet that would be a great choice for a moose would only poke a tiny hole in the ground hog, probably leaving it to die from infection, or less commonly, survive.

You start with your goals, and then work backwards from there to determine the ideal external and terminal ballistics for those goals. That information informs bullet diameter, weight, construction as well as the cartridge specifics.

It turns out that for the very different ballistic situations that 10mm Auto and 30-06 solve for, 180 grains ends up being a pretty solid all around bullet weight or both cartridges. But the bullet construction is very different to accomplish their differing goals.

I would also add that since there is a diameter difference, you have to take sectional density into account as well. And note that there aren’t any 305 grain loads for 10mm. In fact the 10mm just plain can’t compete with the 30-06 on sectional density. A 305 grain bullet in 10mm would basically be a projectile with a primer in it’s base.