A firearm is a weapon designed to expel a projectile by the action of highly combustible, gas-generating gunpowder. This includes rifles, handguns, and shotguns, which are collectively referred to as small arms.8 Small arms are relatively simple mechanical devices that share the same basic anatomy, which consists of the handling portion (stock), the breech (the chamber where the bullet is seated and from which the combustive reaction is triggered), and the barrel, which acts as the projectile’s guide. The differences between small arms are largely delineated by the amount of pressure the breech can withstand and the length of the barrel.
Rifles are shoulder-fired weapons engineered to withstand the very high pressures (50,000-60,000 psi) generated from combustion of the gunpowder. They have long barrels (usually > 16 inches) with a spiraled groove cut into the inner lumen that imparts a spin on the bullet, enhancing inflight stability and accuracy. Handguns are basically small rifles with the same engineering features, but with smaller pressure tolerances (20,000-30,000 psi) and shorter barrels.9