Don't even think about it, I can be nerdier, those are CARTRIDGES, not CALIBERS or AMMO.j/k

Standardwar weapons (as inspired by Big Tiny)

1st - .308 Win. Plenty of power, and a short action as opposed to the 30-06's long action, making the .308 better for semi-auto.

2nd - 6.8mm Grendel, Great automatic AR-style weapon for close quarters. Pretty popular with SWAT teams, I believe.

Honorable mention - .45 ACP, great pistol, great submachine guns, and the chamering of the second most important conventionalweapon of WWII, the Thompson submachine gun.