Rifling

Rifling refers to spiral grooves that have been formed into the barrel of a firearm. It is the means by which a firearm imparts a spin to a prjectile to gyroscopically stabilize it to improve accuracy. Most rifling is created by either cutting with a machine tool, pressed by a tool called a "button" or forged into the barrel over a "mandrel". The grooves are the spaces that are cut out, and the resulting ridges are called 'lands'. These lands and grooves can vary in number, depth, shape, direction of twist ('right' or 'left'), and 'twist rate' (turns per unit of barrel length).

Related Topics:
Firearm - Gyroscopically - Machine tool - Pressed - Forge - Barrel - Twist rate

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The spin imparted by rifling significantly improves the stability of the projectile, improving both range and accuracy.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Typically in small firearms, the diameter of the bullet matches the diameter of the cirlce that encompasses the bottoms of the rifled grooves. When the cartridge is fired, the bullet is forced into the barrel and the rifling engages the bullet, deforming it somewhat. As the bullet is propelled down the barrel, it begins to spin. This rate of spin is dictated by a bullet's muzzle velocity and the twist rateof the rifling. For a given caliber, faster rates of twist are needed to stabilize longer(heavier)bullets.

Related Topics:
Cartridge - Twist rate

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Smooth-bore firearms muskets require bullets that are the same diameter or less than the diameter of the bore. The energy from the discharge upsets or obdurates the bullet and expands it to form a tight seal in the musket. Rifling allows tight-fitting over-bore bullets to be squeezed into the barrel. This allows for higher pressures and longer range for rifles.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

A perfectly formed bullet would have the axial center of its rotating mass coincide with the axial center of its form. To the extent that these two axises differ, the flight path of the spinning bullet takes the form of an expanding cone due to gyroscopic forces. As the twist rate increases, so does the size of the "cone of inaccuracy". Therefore, increasing the twist rate beyond that required to stabilize the bullet is counterproductive.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~