If you are asking what CARTRIDGE fires a bullet at the highest speed, the quickest current (Jan 2014) FACTORY rifle cartridge is the .204 Ruger, with a claimed velocity of 4,225 feet per second. However, the .220 Swift, factory loaded to 4213 fps, can be handloaded with light bullets and driven to speeds of 4,400 fps.
While not a typical firearm, the 120mm Rhinemetall cannon used on the Abrams and Leopard tanks is capable of driving a shell at speeds of 5,700 fps.
Depends on the firearm, the manual or even the box most likely says what the FPS is.
4-6K fps
About 1000 fps for a pre-charged pneumatic, such as the Evanix.
The highest velocity of an airgun is that of Evanix AR6 pistol which is 1000 fps.
Its 1984 fps
No such law
Evanix hunting master model AR6
That would most likely be the Hatsan AT P2 PCP Air Pistol at 870 FPS
In Canada any "gun" that shoots a projectile at 500 FPS or more is considered a firearm.
Bullets alone have no velocity. The .223 CARTRIDGE, when fired from an M16 rifle, will drive its bullet at about 3,200 fps. However, velocity depends on the makeup of the cartridge (powder charge, bullet weight) , and which firearm it is fired from.
Difficult to answer. For a standard cartridge, it is probably the Ruger .204, with a claimed muzzle velocity of 4225 FPS. However, the Remington Accelerator in 30-06 (firing a .25 cal bullet held in a plastic sabot) claimed speed of around 4500 fps. There have been a few wildcat loads that claim around 5000 fps- which is about at the limit of acceleration that smokeless powder can produce.
It can vary from 900-1300 FPS depending on the weight and the firearm. Generally a smaller slug can have a greater velocity and a greater energy.