Sub-caliber ammunition (also spelled subcaliber) is firearm ammunition where the projectile has a smaller diameter than the bore of the gun barrel from which it is fired. Firing sub-caliber ammunition has several potential benefits compared to full-caliber ammunition. It can for example allow for much higher muzzle velocities due to smaller lighter projectiles being fired from relatively larger propellant charges,[1] but it can also lower the cost of ammunition due to less material being used to produce the round compared to a full-caliber ammunition etc.
Several methods exist for firing sub-caliber ammunition.[1]