page_title: Squeeze bore
section_title: Mechanism
hierarchical_section_title: Squeeze bore / Mechanism
caption_attribution_description: English: Illustration of "German 7.5 cm Pak 41 A.P.B.C./T. SHOT."
context_page_description: A squeeze bore also known as a taper-bore, sometimes cone barrel or conical barrel is a weapon where the internal barrel diameter progressively decreases towards the muzzle resulting in a reduced diameter round with an increased velocity.
context_section_description: A squeeze bore utilizes the energy of the propellant to squeeze the diameter of the bullet or shell down, increasing penetration and velocity significantly.  This process also meant high chamber pressure and low barrel service life.  For example, the service life of a squeeze bore 7.5 cm Pak 41 could be as low as 1000 rounds compared to 5000-7000 rounds for the 7.5 cm Pak 39 (L/48).  The diameter of a fired shell could decrease as much as 40% from .50 caliber to .30 caliber (M2 machine gun).  Rather than squeezing solid shot, this is accomplished through a hardened penetrator core (tungsten for example) and a softer outer jacket (aluminium alloy) forming flanges or wings.  This outer jacket was crushed as the projectile left the barrel.
  The squeeze bore concept typically was used in anti-tank guns before the widespread use of shaped charges.  Later, the perfection of discarding sabot ammo, which is based on the same concept of using a larger caliber barrel to fire a smaller caliber projectile at high-speed, negated the need for the squeeze bore concept.
caption: An example of armor-piercing composite non-rigid (APCNR) shells used in squeeze bore guns (7.5 cm Pak 41)
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