Sub-caliber ammunition


Sub-caliber ammunition is firearm ammunition in which the diameter of the projectile is smaller than the bore of the gun barrel from which it is fired. Sub-caliber ammunition has several capabilities that full-caliber ammunition does not. For example, it can achieve a higher muzzle velocity than a full-caliber projectile from the same propellant charge, while costing less because of the smaller amount of material used.
Several methods exist for firing sub-caliber ammunition.

Sabot method

The most traditional way to fire sub-caliber ammunition is to fit the projectile with an expendable sabot. The sabot is a device which fills out the missing caliber when the projectile is fired and then leaves the projectile once it has left the barrel.

Saboted sub-caliber ammunition types

  • Armour-piercing discarding sabot
  • Armour-piercing fin-stabilized discarding sabot
  • Saboted light armor penetrator
  • Flechette
  • Shotgun shell

    Flange method

A common method during World War Two, often called the Gerlich-, Littlejohn- or tapered bore principle, was to fit sub-caliber ammunition with soft metal flanges filling out the missing caliber and then fire them from squeeze bore barrels. Squeeze bore barrels, often found on shotguns, progressively decreases its bore diameter towards the muzzle, resulting in a reduced final bore. When fired the flanges on the projectile would fold inwards as it travels through the reducing inner diameter of the squeeze bore.

Flanged sub-caliber ammunition types

  • Armor-piercing composite non-rigid
  • Armor-piercing non-rigid

    Sub-caliber barrel

A third method is to simply fit a smaller barrel into the original full caliber weapon which then allows the firing of smaller caliber cartridges. This is called sub-caliber training and it is used to lower the cost of training with large caliber weapons by allowing them to fire cheaper lower caliber ammunition and to not put wear on the original barrel.