The person is usually called "the starter."
The "starter"
Impossible to answer without a detailed descripiton of the activity.
The starter.
{| |- | Men who work with cannons are referred to as artillerymen. Cannoneers is another name sometimes used. In an artillery gun crew, the gun captain usually fires the weapon. |}
A sub-machine gun fires pistol cartridges. A machine gun fires rifle rounds.
The people who fire the gun to start the race.
BB gun. Fires a round BB.
To hear the gun shot at the start of the race
The Railgun, it fires over double the speed of sound.
Artillery
No. They trap and slow the release of gasses after the gun fires.
The Dillon Aero M134 Gatling gun fires either 2000 or 4000 rounds per minute, it is selectable.