Bring back the cheap surplus ammo!
If there was one type of rifle surplus ammo you could bring back and have it cheap again, what would it be? I know we'll never see it again, but since hindsight is 20/20 which is your pick?
.30-06, 8mm Mauser, .303 British, 7x57, 7.5x55, 6.5x55, 7.62x39, etc.
If I could buy only one to stockpile, it would have been 6.5x55 or 7x57. I like my .30 calibers, but those middle calibers are much easier to shoot.