Squeeze bore

Mechanism

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 means 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 (achieved in a version of the 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 is crushed as the projectile leaves 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.

History and usage

The squeeze-bore concept was first patented by German inventor Carl Puff in 1903,{{cite patent

In 1939–40, Mauser-Werk AG produced the 2.8 cm sPzB 41 and Krupp (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. Imperial Japan would attempt to create their own version of the Pak 41, known as the Type Ge, but it would not enter production.

Other uses of the squeeze bore include the British Littlejohn adaptor, a QF 6-pounder adapter, and a version of the M2 machine gun produced during WW2, 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 the QF 2-pounder and was designed by František 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 without blank-firing adapters using blank rounds as the pressure is congregated at the muzzle.

Gallery

File:The British Army in Sicily 1943 NA4961.jpg|2.8 cm sPzB 41 squeeze-bore anti-tank gun captured by British forces in Sicily 1943. File:Armata przeciwpancerna Pak 41 kal 42 mm na ulicy włoskiego miasta (2-2100).jpg|4.2 cm Pak 41 light squeeze-bore anti-tank gun in Italy 1943. File:German 10,5 cm squeeze bore.png|A German 10 cm schwere Kanone 18 with an 8,8 cm squeeze-bore adapter attached to the muzzle. File:Tanks and Afvs of the British Army 1939-45 KID4781.jpg|An Mk VII Tetrarch Mk I with a squeeze-bore Littlejohn adaptor.

References

References

1. Rollof, Yngve. (1953). "Artillerimaterielens utvecklingstendenser under senaste decenniet". Tidskrift i Sjöväsendet.
2. (18 February 2017). "Q&A #9: Gas Impingement, Reading List, Squeeze-Bores, and More!". Youtube.
3. "Anti-tank Ammunition Types".
4. (24 April 2018). "Q&A #17: Bullpups, Stocked Pistols, Delayed Blowback, and More!". Youtube.
5. "Exotic Barrels Part 1: Squeeze Bores {{!}} WeaponsMan". WeaponsMan.
6. "Projectile". Free Patents Online.
7. Hogg, Ian V. (1999). "German Secret Weapons of the Second World War". Greenhill Books.
8. (12 January 2011). "Squeeze Bore".
9. (20 May 2016). "Mauser's high-tech antitank gun: the 2.8cm sPzB 41 - The Firearm Blog".