A round is not the same thing as a bullet. A round of ammunition has 4 components. The bullet is the projectile that comes out of the barrel when you pull the trigger, The primer is the component that ignites the powder when it is struck by the firing pin or striker. When the powder is ignited by the primer it burns rapidly which creates expanding gasses that push the bullet out of the barrel. When you combine a case containing the correct amount of powder along with a primer to ignite the powder and a bullet inserted into the case you have a round of ammo. A bullet is not the same thing as ammo. Without the other 3 components a bullet is just a harmless chunk of lead.
A round is loaded into a gun. The gun is then cocked and then fired.
Sorry, but we need more information on the term "round barrel gun".
BB gun. Fires a round BB.
A "Round" is usually how many shots are in the loading chamber. it can be one or many. A BB gun can carry 100 ROUNDS but only fires one ROUND at a time. A Machine gun fires many rounds in a "burst".
the measurements of a round are not measured in that way, nor does the size of the gun have anything to do with how powerful it is
You must specify whether you mean in a long gun or a hand gun.
What model BB gun are you asking about.
Type of rifling/twist.
The event that sparked the recent round of gun control talks was when a boy brought a gun to school and killed twenty children and seven adults. Have a good day!