Asqueeze bore, alternativelytaper-bore,cone barrel orconical barrel, is a weapon where the internalbarrel diameter progressively decreases towards themuzzle, resulting in a reduced final internal diameter. These weapons are used in conjunction with specialsub-caliber ammunition where the projectile is fitted with soft-metalflanges which fills out the caliber.[1] 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.[1]
A squeeze bore utilizes the energy of thepropellant to squeeze the diameter of thebullet orshell down, increasing penetration and velocity significantly. This process also means high chamber pressure and low barrel service life.[2] For example, the service life of a squeeze bore7.5 cm Pak 41 could be as low as 1000 rounds compared to 5000–7000 rounds for the7.5 cm Pak 39 (L/48).[3] The diameter of a fired shell could decrease as much as 40% from .50 caliber to .30 caliber (achieved in a version of theM2 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 is crushed as the projectile leaves the barrel.[4][5]
The squeeze-bore concept typically was used in anti-tank guns before the widespread use ofshaped charges.[4] Later, the perfection ofdiscarding-sabot ammo, which is based on the same concept of using a larger-caliber barrel to fire a smaller-caliber projectile at high speed, negates the need for the squeeze-bore concept.[2]
The squeeze-bore concept was first patented by German inventor Carl Puff in 1903,[7][8] even though the general principle was known already in 19th century and later applied in lighter fashion onArmstrong guns, on which only the muzzle (not the barrel itself) was of slightly smaller diameter (to cast off the sealing leather bag that the powder cartridge was folded into). Later, Hermann Gerlich in the 1920s and 1930s experimented with the concept, resulting in an experimental 7-centimetre anti-tank rifle with a 1,800-metre-per-second (5,900 ft/s) muzzle velocity. This led to the squeeze-bore concept sometimes being called the "Gerlich principle". He also made and sold hunting rifles based on the principle.[9]
In 1939–40,Mauser-Werk AG produced the 2.8 cm sPzB 41 andKrupp (in 1941) produced the 7.5 cm Pak 41. These were eventually discontinued due to the lack of tungsten and manufacturing complexity for the ammunition.[2][10][11]
Other uses of the squeeze bore include the BritishLittlejohn adaptor, aQF 6-pounder adapter, and a version of theM2 machine gun produced during WW2,[5] Squeezing down from 40mm to 30mm, 57mm to 42.6mm, and .50 caliber to .30 caliber respectively. The Littlejohn adapter was used to extend the service life of theQF 2-pounder and was designed byFrantišek Janeček whose anglicized name gave the Littlejohn its designation. The QF 6-pounder adapter was never adopted.
Firearms with Squeeze bore barrels are more likely to function withoutblank-firing adapters using blank rounds as the pressure is congregated at the muzzle.[citation needed]
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![A German 10 cm schwere Kanone 18 with an 8,8 cm squeeze-bore adapter attached to the muzzle.[1]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aGerman_10%2c5_cm_squeeze_bore.png)
Squeeze bore artillery