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Squeeze bore
Squeeze bore
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Historical squeeze bore example:
7.5 cm Pak 41 squeeze bore gun
7.5 cm Pak 41 flange-projectiles.
Left: Armor-piercing composite non-rigid (APCNR)
Right: Armor-piercing (AP)

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.[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]

Mechanism

[edit]
Diagram of the squeeze-bore concept

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.[2] 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).[3] 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.[4][5]

The squeeze-bore concept typically was used in anti-tank guns before the widespread use of shaped charges.[4] 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, negates the need for the squeeze-bore concept.[2]

History and usage

[edit]
The original patent filed by Hermann Gerlich in 1932[6]

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 on Armstrong 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 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.[2][10][11]

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,[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 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.[citation needed]

[edit]

See also

[edit]

Squeeze bore artillery

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Squeeze bore

View on Grokipedia
from Grokipedia
A squeeze bore, also known as a tapered bore or Gerlich gun, is a specialized or barrel design in which the internal progressively decreases from the breech end to the muzzle, compressing a fitted to reduce its and thereby increase and penetration capability. This tapering can occur throughout the barrel length or only in a muzzle section, allowing the propellant's gases to act on a larger initial surface area for enhanced acceleration while minimizing air resistance at exit. The projectiles for such weapons feature a deformable structure, often including soft metal flanges, a , or a spool-like body at the rear, which seals against the bore and is forged down in diameter during travel to maintain gas pressure and achieve hypervelocities. Named after German engineer Hermann Gerlich, who advanced the concept in the and through s and experimental designs, the squeeze bore principle originated from earlier ideas like Karl Puff's 1903 but gained practical form in Gerlich's high-velocity rifles and anti-tank prototypes. Primarily employed in experimental high-velocity guns for anti-tank roles, the design offered advantages in performance by leveraging energy more efficiently, though challenges such as increased barrel wear, complexity, and manufacturing difficulties restricted it to limited military applications. for squeeze bore firearms, such as Gerlich taper bore cartridges, remains classified as curios or relics under U.S. regulations.

Mechanism and Design

Operating Principle

A squeeze bore, also known as a tapered-bore or Gerlich , features a barrel in which the internal diameter progressively decreases from breech to muzzle, typically by 20-25%, creating a conical profile that compresses the during its travel. This design, often implemented as a smooth-bored muzzle extension attached to a standard , utilizes the propellant's energy to deform and accelerate the without discarding components. The operating process begins with ignition of the , generating high-pressure gases that propel the sub-caliber forward through the initial larger- section of the bore. As the enters the tapering portion, the reducing compresses a malleable outer jacket encasing a rigid core, folding protruding flanges or studs inward and sealing the bore to minimize gas escape. This deformation reduces the 's effective while converting some energy into plastic work on the jacket, allowing the remaining energy to accelerate the now-lighter to higher velocities, such as increasing from ~900-1,100 m/s in comparable standard guns to 1,100-1,400 m/s in squeeze bore implementations. Fundamentally, the physics relies on from the propellant gases, where the total work performed includes both acceleration and jacket deformation, rather than acceleration alone; chamber pressures up to 5000-6000 facilitate the necessary deformation without excessive gas leakage past the compressing sections. The gas dynamics maintain a near-constant along the taper, enhancing acceleration as the cross-sectional area decreases, akin to a converging . Many squeeze bore designs dispense with in the tapered section, as the continuous compression and centering action of the converging walls provide gyroscopic stability to the , preventing yaw and ensuring straight travel without spin-induced rotation. For instance, the German Pak 41 integrated this via a smooth tapered adapter to achieve enhanced performance.

Projectile Construction

The projectiles designed for squeeze bore systems feature a optimized for deformation during passage through the tapered barrel, consisting of a hardened core for armor penetration encased in a softer jacket or sleeve made of aluminum or that yields under without fragmenting. This core is surrounded by the deformable outer layer to initially fill the larger chamber diameter while allowing compression to the sub-caliber muzzle size. Key design elements include a spool-like or fluted base configuration with external flanges or skirts—often perforated in the forward section—to promote uniform squeezing and maintain gas seal without traditional driving bands, as is typically absent in these weapons. Some variants incorporate a mild screw-head for assembly and a ballistic cap of or similar to protect the nose during flight, along with a base tracer for observation. Unlike discarding sabot rounds such as APDS, the squeeze bore projectile's deformation is achieved integrally via the jacket's interaction with the barrel taper, without separate discardable components. Manufacturing these projectiles presented challenges in precision molding the jacket to ensure even radial compression and avoid uneven stress that could cause instability or failure, requiring specialized swaging or casting techniques for the soft alloy components around the rigid core. A representative example is the 28 mm projectile for the sPzB 41, featuring a tungsten carbide core approximately 40 mm long and 11 mm in diameter within an aluminum jacket, with a total projectile weight of 130 g. For larger calibers, the 75 mm Pak 41 APCNR round employs a 0.91 kg tungsten carbide core (1.16 inches in diameter) in a 2.58 kg aluminum-bodied projectile with rear flanges and a perforated forward skirt, totaling 2.58 kg. The jacket's deformation in flight reduces the projectile's frontal area by approximately 20-30% from the initial chamber , thereby concentrating on the core to enhance armor penetration while preserving overall stability. This interaction with the barrel's taper, as described in the operating principle, ensures the core emerges streamlined for optimal ballistic performance.

Barrel and Ammunition Specifications

Squeeze bore barrels were constructed from high-strength alloys to endure the extreme pressures generated during firing, typically in the range of several thousand atmospheres, with designs emphasizing precision machining to maintain the precise taper profile essential for deformation. For instance, the featured a barrel of approximately 1.73 (including ), tapering from 28 mm at the chamber to 20 mm at the muzzle over roughly 50 calibers, resulting in a total of 2.69 and a weight of 229 kg. Similarly, the had a total barrel of 4.32 , with a rifled bore section of 2.95 followed by a 0.95-meter tapered extension that reduced the diameter from 75 mm to 55 mm, incorporating progressive tapers of 1:20 over 270 mm and 1:12 over 170 mm, and a total weight of 1,356 kg. Ammunition for these systems utilized bottlenecked brass cartridge cases to accommodate high-pressure propellants, ensuring reliable and gas sealing within the tapered chamber. The 2.8 cm Pzgr. 41 round for the sPzB 41 weighed about 0.13 kg per , with a full cartridge employing nitrocellulose-based to achieve muzzle velocities up to 1,400 m/s, though specific propellant loads were not publicly detailed in wartime manuals. For the PaK 41, the 7.5 cm PzGr 41 HK armor-piercing round featured a 544 mm case length, a 7.8 kg with tungsten core and aluminum sabot, and a charge yielding 1,125 m/s velocity; a steel-core variant (PzGr 41W) weighed 7.7 kg and reached 1,210 m/s. The 4.2 cm PaK 41, a lighter variant, tapered from 42 mm to 28 mm and fired armor-piercing squeeze-bore (APCNR) at 1,265 m/s. Design variations included both fully smoothbore tapers for simplicity and hybrid configurations with initial to impart spin before the squeezing phase, as seen in the PaK 41's early rifled section transitioning to . reductions were consistent across models, such as 28/20 mm for the sPzB 41 and 75/55 mm for the PaK 41, with the reducing from 42 mm to 28 mm over 55.8 . Experimental adaptations explored even smaller scales, though production focused on anti-tank roles. Tolerances in barrel fabrication demanded sub-millimeter precision for the taper to ensure uniform compression without jamming or excessive , often requiring specialized tooling unavailable in standard production. Barrel was accelerated due to the high frictional forces, limiting to 500–1,000 rounds for the PaK 41 before accuracy degraded significantly, with the sPzB 41 lasting approximately 500 rounds. Maintenance involved regular inspection for taper integrity, as could reduce velocity and penetration by altering the bore profile. These specifications rendered squeeze bore incompatible with conventional firearms, as the unique chambering and sabot designs prevented interchangeability, necessitating dedicated chains that contributed to their limited adoption.

Historical Development

Early Concepts and

The squeeze bore concept, involving a tapered barrel that compresses a deformable jacket to enhance , was first conceptualized in the early by German inventor Karl Puff. In , Puff filed a for a barrel featuring an initial parallel section followed by a gradual taper toward the muzzle, designed specifically to accelerate sub-caliber s in by deforming their soft metal jackets under gas pressure. This design, detailed in Austrian Patent AT 34367 titled "Lauf für Handfeuerwaffen und Geschütze" (Barrel for and guns), was published on July 20, 1906, and issued on April 15, 1908, marking the initial formal documentation of the technology. An equivalent British filing, Patent No. 8601 dated August 27, 1904, included illustrations of the tapered bore applied to a , emphasizing its potential for higher velocities through sustained chamber pressure. Puff's theoretical groundwork highlighted the energy efficiency of jacket deformation as an alternative to conventional expansion against a parallel bore, where gas typically drives the via expanding driving bands. By squeezing the jacket inward, the design aimed to minimize gas leakage and prolong effective , theoretically converting more propulsive into kinetic rather than radial expansion. This approach was envisioned for proof-of-concept applications in , with the describing sub-caliber encased in malleable alloys to withstand the taper without fragmentation. Early recognition of these principles positioned squeeze bore as a promising method for improving small arms performance, though practical testing remained limited to conceptual demonstrations prior to . Key challenges identified in Puff's work centered on material science limitations, particularly the need for jacket alloys ductile enough to deform uniformly without rupturing under , while maintaining structural integrity for accurate flight. Barrel durability also posed issues, as the tapered geometry risked accelerated wear from the concentrated forces of deformation, requiring advanced unavailable at the time. These hurdles prevented widespread implementation in the pre-war era, confining the innovation to theoretical and experimental stages. Puff's foundational patent influenced subsequent designs, serving as a reference for later engineers despite its lack of immediate practical adoption until the 1920s. Notably, it provided the conceptual basis for Hermann Gerlich's refinements in tapered bore systems for hunting rifles and anti-tank applications.

Interwar Advancements

During the interwar period, German engineer Hermann Gerlich advanced squeeze bore technology through his development of the "Gerlich rifle" in the 1920s, a tapered-bore sporting firearm that achieved muzzle velocities up to approximately 1,200 m/s with specialized ammunition, demonstrating the principle's potential for high-speed projectiles. Building briefly on earlier patents such as Karl Puff's 1903 design, Gerlich's innovations were tested in experimental 7 mm anti-tank rifle configurations, which recorded velocities around 1,400 m/s and highlighted the system's applicability to military anti-armor roles. These efforts, conducted largely in collaboration with firms like Halbe under the Halger brand, emphasized lightweight, high-velocity designs suitable for portable weapons, though initial applications remained focused on civilian and prototype testing due to post-World War I restrictions. In , following Gerlich's in a testing accident, the conducted trials of squeeze bore prototypes, including evaluations of scalability for applications. These trials, part of clandestine rearmament efforts, evaluated the technology's feasibility for support but revealed challenges in reliability and production scalability. Concurrently, material innovations emerged, such as the use of cores encased in aluminum alloy jackets for projectiles, which allowed the deformable outer layers to conform to the tapering barrel while preserving the hard penetrator's integrity for enhanced armor-piercing performance. International interest in Gerlich's work grew during this era, with prototypes trialed in the , , and , though adoption remained limited due to the system's mechanical complexity and high manufacturing demands compared to conventional firearms. , however, acquired Gerlich's Halger rifle in 1931 for testing, which informed the development of the domestic , a conventional high-velocity achieving approximately 1,275 m/s. Progress in was slowed by economic constraints from the , which capped military spending and personnel at 100,000 troops while prohibiting heavy weapons development, forcing into secretive and underfunded channels. Additionally, the Wehrmacht's prioritization of conventional , such as the standard 3.7 cm Pak 35/36, diverted resources toward proven, mass-producible designs amid rapid rearmament needs.

World War II Implementations

The squeeze bore principle, building on interwar prototypes by Hermann Gerlich, saw its first major wartime implementation in with the introduction of the 2.8 cm schwere Panzerbüchse 41 (sPzB 41) in , entering service in 1941 as a response to escalating armored threats like the Soviet . This lightweight, portable weapon was designed for and motorized units, providing high-velocity fire to penetrate thicker armor at range. Production by Mauser-Werke AG ramped up from 1940, yielding a total of 2,797 units by 1943, though early output was modest at 94 guns in 1940 and 349 in 1941. In 1941, expanded squeeze bore applications with the , a heavier intended for mounting on and IV tanks as well as towed use, further addressing the armor challenges posed by T-34s and similar designs on the Eastern Front. Approximately 150 units were produced, limited by the technology's demands, with deployment focusing on key theaters including , where sPzB 41 crews supported operations against British armor, and the Eastern Front, where both weapons contributed to defensive actions against Soviet advances. These guns offered superior muzzle velocities for their caliber, enabling effective engagement at distances up to 500 meters against sloped armor. Resource constraints severely hampered squeeze bore proliferation, particularly acute tungsten shortages by 1942, as the Panzergranate 41 (Pzgr 41) projectiles relied on cores for optimal penetration. To mitigate this, German engineers developed steel-core alternatives, which sacrificed velocity and armor-piercing capability, reducing effectiveness against heavy tanks by up to 30% at typical combat ranges. Production of both sPzB 41 and Pak 41 ceased in 1943, totaling around 2,950 squeeze bore guns overall, due to these material shortages combined with the manufacturing complexity requiring specialized precision machining and skilled labor that strained wartime industry. The shift favored simpler, more producible designs like the , which used conventional rifled barrels and steel-based ammunition, allowing mass output exceeding 20,000 units without rare materials.

Applications and Performance

German Anti-Tank Weapons

The 2.8 cm schwere Panzerbüchse 41 (sPzB 41) was a lightweight developed by Mauser-Werke, weighing 229 kg in its towed configuration, which allowed for easy manhandling by a small crew. It featured a tapered barrel reducing from 28 mm at the breech to 20 mm at the muzzle, firing the 2.8 cm Pzgr. 41 armor-piercing discarding sabot round with a core at a of 1,400 m/s, achieving penetration of approximately 40 mm of armor at 500 m. This design provided effective short-range anti-tank capability for infantry units, particularly against medium tanks like the Soviet T-34's side armor during early encounters on the Eastern Front. The sPzB 41 entered service in 1941 and was issued to anti-tank and pioneer units, with production totaling around 2,800 units before being phased out by 1943 due to obsolescence against heavier Allied armor. included the primary APCNR (armor-piercing composite non-rigid) round for anti-tank roles, supplemented by limited high-explosive variants that proved ineffective for fragmentation. The gun's barrel had a of about 500 rounds, limited by rapid erosion from the high-velocity projectiles. Variants of the sPzB 41 included vehicle-mounted installations for enhanced mobility, such as on the , which carried 168 rounds and served in reconnaissance and infantry support roles, and the lighter Sd.Kfz. 221 armored car for rapid deployment. A version without suspension was also produced for airborne operations. The heavier 7.5 cm Panzerabwehrkanone 41 (PaK 41), produced by starting in 1942, weighed 1,410 kg and was primarily a towed , though its bulk reduced tactical flexibility compared to lighter conventional anti-tank weapons like the 7.5 cm PaK 40. Employing a squeeze-bore mechanism tapering from 75 mm to 55 mm, it fired the 7.5 cm Pzgr. 41 (HK) APCR round at 1,130 m/s, penetrating up to 145 mm of armor at 1,000 m at 30° obliquity, making it highly effective against heavy tanks such as the KV-1 during operations in the and Orel sectors. Ammunition types focused on APCR with cores for maximum velocity, though tungsten shortages later forced substitution with steel-cored rounds that reduced performance. The PaK 41 saw limited production of about 150 units and was deployed mainly on the Eastern Front from to 1943, supporting infantry divisions in defensive anti-tank roles but suffering from high manufacturing complexity and barrel erosion limiting service life to 500-1,000 rounds. While no widespread mountings were adopted, experimental self-propelled variants on chassis were tested for greater mobility. Both weapons exemplified German efforts to counter escalating armor through squeeze-bore technology, providing with potent but specialized anti- support during the critical 1941-1943 period, though their short barrel life and constraints highlighted practical limitations in sustained operations.

Allied and Other Adaptations

The British represented the primary squeeze bore adaptation employed by Allied forces during . Originally developed by Czech engineer František Janeček in the late 1930s and brought to Britain following the German occupation of , the device was adopted to enhance the anti- capabilities of existing without requiring full barrel replacements. Production of the Mk I version began in , with the improved Mk II approved in May 1944. The adaptor consisted of a muzzle sleeve approximately 1 foot (30 cm) long with a smooth, tapered internal bore that compressed the during firing. For the QF 2-pounder (40 mm) gun, it reduced the bore diameter from 40 mm to 30 mm; a variant for the QF 6-pounder (57 mm) gun tapered from 57 mm to 38 mm. It was paired with specialized Armour-Piercing Super Velocity (APSV) ammunition, featuring a soft metal sabot and core, which allowed the to deform and pass through the narrowing bore. This design doubled the compared to standard rounds—reaching about 1,200 m/s for the 2-pounder—and increased armor penetration by up to 100% at typical combat ranges, enabling effective engagement of heavier German armor like the at distances beyond 500 meters. The Littlejohn was fitted to towed QF 2-pounder anti-tank guns (upgraded to Mk XA configuration) and vehicle-mounted variants, including the Daimler Armoured Car, , and airborne tank. It also saw limited aerial use on the Hawker Hurricane IID fighter-bomber for ground attack roles. It saw widespread deployment in , , and Northwest Europe from mid-1943 until the war's end in 1945, particularly on Cromwell and Challenger tanks where it extended the utility of obsolescent 2-pounder armaments. However, its effectiveness was hampered by shortages, leading to reliance on less penetrative steel-core alternatives by late 1944, and it was phased out post-war in favor of more versatile 6-pounder and 17-pounder guns. In the United States, the conducted experimental work on a squeeze bore modification for the .50 caliber heavy machine gun during , adapting it for use by reducing the projectile diameter from .50 to .30 caliber to boost velocity. These tests achieved muzzle velocities around 1,200 m/s but were abandoned due to excessive barrel wear and the superiority of conventional high-velocity ammunition. Soviet interest in squeeze bore technology dated back to the , with conversions of Berdan rifles tested in the , but no production followed; during , evaluations of captured German examples occurred, yet no indigenous systems reached service due to prioritization of simpler anti-tank designs like the PTRD rifle. Allied forces, particularly the British, emphasized squeeze bore adaptors as cost-effective retrofits for legacy guns, conserving industrial resources and production lines amid wartime demands while providing a quick upgrade path against evolving armored threats—unlike full redesigns, these attachments could be field-installed in hours and utilized existing ammunition stocks with minimal modification. Limited trials by other nations included Japanese experiments with tapered-bore anti-tank cannons in the early 1940s, inspired by German designs, but these yielded no operational weapons due to material constraints and reliability issues.

Advantages and Limitations

Squeeze bore technology offered significant ballistic advantages over conventional parallel-bore anti-tank guns, primarily through its tapered barrel design that compressed the projectile's flanges, resulting in substantially higher muzzle velocities. For instance, the 7.5 cm Pak 41 achieved a muzzle velocity of 1,125 m/s with its tungsten-cored PzGr 41 round, representing approximately a 42% increase compared to the 792 m/s of the standard 7.5 cm Pak 40. This velocity boost translated to enhanced armor penetration, with the Pak 41 capable of defeating up to 177 mm of armor at 1,000 m and 0° obliquity, far surpassing the Pak 40's approximately 96 mm under similar conditions or the Pak 38's roughly 100 mm. Additionally, the flatter trajectory enabled effective engagement ranges extending to 2,000 m, improving accuracy and lethality against armored targets at longer distances. Despite these performance gains, squeeze bore systems suffered from critical limitations that restricted their widespread adoption and operational utility. The high chamber pressures required for the squeezing effect accelerated barrel , limiting to as few as 500–1,000 rounds for the Pak 41, in contrast to over 6,000 rounds for the Pak 40; this wear often led to progressive inaccuracy as the tapered section deformed. complexity, involving precision of the tapering bore and specialized sub-caliber projectiles, drove up costs—approximately 15,000 Reichsmarks per Pak 41 unit versus 12,000 for the Pak 40—resulting in low production totals of only about 150 guns. was particularly sensitive, with the soft jacket surrounding the tungsten core prone to deformation during storage or handling, further complicating . Moreover, the design's heavy reliance on scarce for the penetrator cores became a fatal flaw, as supply shortages from disrupted imports halted production by mid-1942 and rendered stockpiles unusable without alternatives. Overall, while squeeze bore weapons like the Pak 41 proved highly effective for mid-war anti-tank roles on fronts such as the Eastern Front in 1942–1943, their operational drawbacks—including rapid wear, high costs, and material dependencies—limited scalability and contributed to obsolescence by late , as simpler high-velocity designs with composite emerged as more sustainable alternatives.

Legacy and Comparisons

Post-War Developments

The saw use during on light armoured vehicles such as the Daimler armoured car, which remained in service through the and into the early . However, the adaptor was phased out post-war by the mid-1950s in favor of (APDS) ammunition, which provided comparable or superior penetration while allowing the use of high-explosive and other multi-purpose rounds from standard rifled barrels. In the United States, post-war experiments focused on adapting squeeze bore principles to increase firepower from existing machine guns, particularly the .50 caliber . The Salvo Squeeze Bore (SSB) project, developed primarily by Colt in the 1950s and 1960s, involved tapering the barrel to compress multiple .50 caliber subprojectiles down to .30 caliber, enabling salvo fire of 3 to 6 rounds per cartridge to simulate higher rates of fire for anti-personnel and light anti-armor roles, including potential aircraft applications. These trials were ultimately rejected due to reliability concerns, such as inconsistent subprojectile separation and excessive barrel erosion from the high pressures involved. Soviet post-war research included prototypes for squeeze bore conversions on and automatic weapons, such as a gas-operated 37/25 mm developed by TsKB-14 between 1946 and 1948, intended for belt-fed anti-tank and anti-aircraft use with a cyclic rate of 300-350 rounds per minute. These efforts did not progress to widespread adoption, remaining experimental amid shifting priorities toward more conventional designs. No major military programs adopted squeeze bore technology after the , with interest limited to niche civilian collectors seeking rare ammunition like .50/30 caliber SSB rounds. The decline stemmed from inherent drawbacks, including rapid barrel wear and the inability to fire versatile ammunition types, compounded by the maturation of APDS rounds and the emergence of shaped-charge warheads that offered better penetration without specialized barrels. By the late , the rise of composite armors further diminished the relevance of high-velocity kinetic penetrators like those enabled by squeeze bores, while guided munitions provided precision alternatives for anti-armor roles.

Comparisons to Modern Technologies

Squeeze bore technology shares conceptual similarities with and rounds in employing sub-caliber projectiles to enhance penetration through reduced cross-sectional area and increased velocity. However, while APDS and APFSDS utilize a sabot that supports and centers the dense penetrator core during in-barrel before discarding it immediately after exiting the muzzle, squeeze bore systems deform the projectile's outer inward via a tapering barrel to achieve the sub-caliber effect directly within the bore. This fundamental difference renders APDS/APFSDS designs simpler mechanically, as they avoid the need for deformable projectile materials and the associated manufacturing complexities, while also extending barrel life compared to the rapid wear experienced in squeeze bore guns, such as the 7.5 cm PaK 41's limitation to approximately 500 rounds before replacement. In comparison to conventional rifled guns firing full-caliber rounds, squeeze bore offered a velocity advantage during —reaching around 1,130 m/s for the PaK 41's Pzgr. 41 projectile—but this edge has been surpassed by modern fin-stabilized APFSDS rounds, which achieve muzzle velocities of 1,500–1,800 m/s through optimized propellants, longer barrels, and configurations that minimize drag on the long, slender penetrators. The stabilizing fins in APFSDS eliminate the need for rifling-induced spin, allowing for higher velocities and flatter trajectories without the barrel erosion inherent to squeeze bore's tapering design. Squeeze bore has become irrelevant in contemporary military applications, supplanted by advanced composite penetrators made from or alloys in APFSDS rounds, which provide superior long-rod penetration, and by precision-guided munitions like anti-tank guided missiles (ATGMs) that prioritize accuracy and standoff range over raw . Hypothetical adaptations for , such as assault rifles, have been dismissed due to the excessive barrel wear, manufacturing intricacy, and negligible performance gains relative to existing subsonic or supersonic ammunition designs. As of 2025, no active programs employ squeeze bore technology. The legacy of squeeze bore lies in its influence on sub-caliber projectile concepts, informing post-war developments in discarding sabot ammunition while being abandoned for more cost-effective alternatives that balanced performance with logistical feasibility. It contributed to foundational ballistics research on energy utilization, particularly in understanding how affects and penetration efficiency, as explored by institutions like the U.S. during and after .

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