This can be influenced by several factors, including operator training level, mechanical limitations, ammunition availability, and weapon condition.
Sustained is the maximum efficient rate of fire given the time taken to load the weapon and keep it cool enough to operate.
For rifles, ease-of-use features such as the design of the bolt or magazine release can affect the rate of fire.
Inside a vehicle, ammunition storage may not be optimized for fast handling due to other design constraints, and crew movement may be constricted.
Artillery rates of fire were increased in the late 19th century by innovations including breech-loading and quick-firing guns.
An example of increase in rate of fire is the Maxim machine gun that was developed in 1884 and used until World War I ended in 1918.
M134 Miniguns mounted on attack helicopters and other combat vehicles can achieve rates of fire of over 100 rounds per second (6,000 rpm).
Sustained rate-of-fire depends on several factors, including reloading, aiming, barrel changes, cartridge fired, and user expertise.
Knowing the effective rate of fire for a weapon can be useful for determining ammunition reserve and resupply requirements.
The term sustained refers to firing a fully-automatic weapon continuously, while rapid is limited to semi-automatic or manually operated firearms.
These fire rates push weapons and soldiers to their physical limits and cannot be sustained for long periods.
A modern machine gun team will carry at least one spare barrel for their weapon, which can be swapped out within a few seconds by a trained crew.
For this and other reasons, weapons with such high rates of fire are typically only found on vehicles or fixed emplacements.