And in the sense of “well regulated” that the Founders meant (meaning accurate, ready, prepared) - they obviously would have put no limits on the amount of ammunition. OR the type of weapon.
“Reporting to duty Sir! I’ll need some guys though if you want my cannon, 1000 balls and the 100,000 rounds of ammunition. Would that help?”
I believe that in colonial times, the militia was expected to show up with rifle and the equivalent of 50 rounds of ammo. Since it would take 20 minutes to half an hour to load and fire 50 rounds from a muzzle loader, that was a considerable amount.