Driving band
The driving band or rotating band is part of an artillery shell, a band of soft metal near the middle of the shell, typically made of gilding metal,[1] copper or lead. When the shell is fired the pressure of the propellant swages the metal into the rifling of the barrel, both providing a seal preventing the gases from blowing past the shell, as well as engaging with the rifling to spin-stabilize the shell. In a rifle, the entire bullet is typically covered in copper or a similarly soft alloy, so the entire bullet is its own driving band.
One downside to the driving band is that it must be placed at the widest point on the shell, and also near the balance point. This is not necessarily the best point from an aerodynamic perspective, at high supersonic speeds the widest point should be far to the rear of the balance point. Another issue is that with increasing shell weight it becomes more difficult to engineer the driving band. Instead of the propellant gases driving the shell up the barrel, it can simply blow the driving band right off the shell.
[edit] Variations
Driving bands pre-cut for the rifling have been used for muzzle loaded weapons, eg some mortars. Freely rotating bands can be used to reduce the amount of spin imparted to the round as is preferable for HEAT warheads or fin stabilised projectiles.
Gerald Bull worked extensively on ways to eliminate the driving band, leading to the development of his Extended Range, Full Bore ammunition using an inversion of the pre-cut rifling for his GC-45 howitzer, which is now rapidly replacing older artillery world-wide.
