why are bullets called rounds instead of just bullets?

ammo, ammunition, ball, bolt, cap, cartridge, dose, lead, love letter, pellet, projectile, rocket, round, shot, slug, trajectile

I agree with Gary s explanation. Historically, bullets were initially round in shape and the name "rounds" has remained as one of the most popular names for the projectiles shot from a gun despite the different shapes of some modern bullets today.

They can't be called just 'bullets' since the round contains the bullet and the charge (explosive) to fire the bullet, and the cap to get the charge going when the pin in the gun strikes it as the trigger is pulled. Though many people think of them as 'bullets', in the armed forces, and in any official capacity, they must be described as rounds.

Perhaps historically from when spheres were used as ammunition instead of the modern bullet we know today, with the casing and everything.

The "rounds" were phased out because they were less accurate and did not travel as far.