Squeeze bore

A squeeze bore, alternatively taper-bore, cone barrel or conical barrel, is a weapon where the internal barrel diameter progressively decreases towards the muzzle, resulting in a reduced final internal diameter. These weapons are used in conjunction with special sub-caliber ammunition where the projectile is fitted with soft-metal flanges which fills out the caliber. As the projectile travels through the squeeze bore, the flanges fold inwards, resulting in a reduced caliber round with an increased velocity compared to a traditional full-caliber round.