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Thompson Autorifle
Thompson Autorifle
Thompson Autorifle
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The Thompson Autorifle, (also referred to as the Thompson Model 1923 Autoloading Rifle; and the .30-06 Model 1923 Semi-Automatic Rifle, among others, etc.) was a semi-automatic rifle that used a Blish Lock to delay the action of the weapon. It was chambered in .30-06, with the 1923 model in 7.62×54mmR Russian rifle rounds.[1]

Key Information

Several prototypes of the Autorifle were submitted by Auto-Ordnance to the military for the semi-automatic rifle trials, but it was not adopted.[2] The Autorifle Model 1929, in .276 Pedersen, was tested in a competition with the rifles by J.D. Pedersen (delayed blowback) and John C. Garand (gas-operated), which culminated in the adoption of the M1 Garand.

On the positive side, the Autorifle action avoided the complexity of recoil-operated and gas-operated actions. On the negative side, the Autorifle required lubricated ammunition for proper functioning and the ejection of spent cartridge casings was so violent as to be hazardous to bystanders.[3]

Function

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For reloading, the Thompson Autorifle uses an interrupted screw delayed blowback operation where the bolt has 85° angled interrupted rear locking lugs that have to overcome a rotation of 110° ( 90° to unlock before the angle blend of 70°/40° and 6°) that delays the action until the gas pressure drops to a safe level to eject. The bolt cocks the striker on opening (a la Mauser) and fires from a closed position. When firing, the trigger when pulled pushes a lever connected to a sear to fire the weapon. The receiver is of a round section with the safety switch at the rear along with the rear sight. The magazine is stripper fed holding 5 rounds and lubricated by oiled pads; later prototypes used 20-round M1918 BAR magazines.[4]

Variants

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BSA Autorifle

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The BSA Autorifle was a British automatic rifle designed by Birmingham Small Arms Co. This rifle was manufactured by BSA under their licensing agreement with the Auto-Ordnance Corp. It was offered for British Army trials during the 1920s.[5]

The weapon was an improved derivative of the Thompson Autorifle that could be operated manually if the two curved 'shutters' around the bolt head are moved into the down position. By this means the mechanism is disconnected and the rifle can be used as a manual loader. This facility was a requirement in self-loaders offered for British trials at this period. The weapon took part in trials during 1927 against a Colt-made Thompson, an 'improved' BSA Thompson, a gas-operated BSA and the Farquhar Hill. Although in 1928 reports it narrowly beat the 'improved' BSA and the Farquhar Hill in the third place, it never advanced past prototype stages as none were found acceptable and development of the BSA Autorifle waned.

BSA Guns Ltd, a licensee of protecting the patents of the Thompson Autorifle made a handful of the 1923 model Thompsons as 'heavy rifles' with folding bipods and finned barrels. Surviving examples suggest there were Rifle and Light Machine Gun variants and 6 of both types were manufactured. The first examples were made in 1924 and an 'improved' variant in 1926. The 'improved' BSA Thompson had a shorter operation with a straight pull cocking handle installed at the rear of a cocking sleeve.

The BSA Autorifle is a delayed blowback–operated rifle chambered in the .303 British round and fed from a removable 10-round box magazine. Much like its predecessor, it uses a bolt with 85° angled threads delayed by a 90° twist to unlock from a bronze nut until the gas pressure drops to a safe level to eject. The bolt cocks the striker on opening (a la Mauser) and fires from a closed position. When firing, the trigger when pulled pushes a lever connected to a sear to fire the weapon. The receiver is of a round section with the safety switch at the rear along with the rear sight.

See also

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References

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Thompson Autorifle

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from Grokipedia
The Thompson Autorifle was an experimental developed in the early 1920s by General and Lieutenant Commander John Blish, utilizing the innovative but flawed Blish principle of friction-based delayed blowback to chamber the powerful cartridge. Designed as a lightweight, magazine-fed infantry weapon to bridge the gap between bolt-action rifles and emerging automatic firearms, the Autorifle featured a long receiver, detachable box magazine, and variants including a fixed internal magazine model and a heavy-barreled configuration with bipod. The Blish lock mechanism relied on the of dissimilar metals under to delay bolt opening, but it proved unreliable with high-pressure .30-06 rounds, necessitating lubricated cartridges and oiled felt pads in the magazine to function without excessive wear or failures. Production was limited, with Colt's Patent Fire Arms Manufacturing Company assembling approximately 20 units of the Model 1923 for U.S. Army Ordnance Department trials in 1924, following earlier prototypes tested in 1920 and 1921. During these evaluations at , the rifle demonstrated violent ejection—capable of embedding spent cases into wooden fixtures—and suffered from bolt breakages, poor endurance, and extraction issues, leading to its rejection by 1929 despite modifications. Though unsuccessful as a , the Autorifle's development laid foundational work for the iconic , shifting focus from .30-06 to pistol rounds where the Blish principle was more viable in lower-pressure applications. Backed by financier through the newly formed , the project highlighted early 20th-century innovations in automatic firearms amid post-World War I military experimentation. Today, surviving examples are rare collector's items, valued for their historical role in the evolution of American small arms design.

History and Development

Origins

Following , retired U.S. Army Brigadier General sought to develop an automatic military rifle to provide infantry with greater firepower, drawing from his observations of limitations and his prior work in ordnance at facilities like and . His vision emphasized a shoulder-fired weapon capable of sustained fire, initially conceptualized as a full-power rifle to supplant or supplement the standard bolt-action , though it later influenced scaled-down designs when rifle-caliber challenges arose. Thompson's ideas built on wartime demands for portable automatic arms, aiming to enable a single soldier to deliver machine-gun-like output without crew-served equipment. To realize this, Thompson co-founded the in 1916 with financier and naval officer John Bell Blish, establishing the company specifically to research and produce automatic firearms for military applications. Headquartered initially in New York with an engineering office in , , Auto-Ordnance focused on innovative mechanisms for reliable automatic operation, securing private investment exceeding $1 million to fund prototyping and testing amid the U.S. Army's post-war interest in semi-automatic rifles. The corporation collaborated with firms like Warner & Swasey for early machining and employed engineers such as Theodore Eickhoff and Oscar V. Payne to refine designs. Central to the project was the principle, patented by John Bell Blish in 1915 and introduced commercially in 1916, which relied on friction-based adhesion between dissimilar metals—typically and —under high pressure to delay bolt movement in a blowback . Blish joined Auto-Ordnance to adapt his mechanism for use, initially demonstrating it in a modified before applying it to higher-pressure rifle cartridges. This friction-delayed blowback action was selected to simplify operation compared to gas or , though it proved challenging with full rifle power. The initial design goals centered on a for standard infantry issue, chambered in the cartridge to ensure compatibility with U.S. service ammunition and logistics. Conceptual work intensified around 1920, with Auto-Ordnance producing early experimental models that year, followed by more refined prototypes submitted for U.S. Army trials by 1921. By 1923, the first production-oriented prototypes, including the Model 1923 manufactured by Colt's Patent Fire Arms Manufacturing Company, emerged as viable testbeds for the Blish system in a full-length configuration.

Prototypes and Trials

The development of the Thompson Autorifle's 1923 prototype marked a significant step in its evolution as a chambered in , with Colt Firearms Manufacturing Company producing a limited batch of 20 units specifically for testing purposes. These prototypes, completed in 1923, incorporated the mechanism for delayed blowback operation and were designed as semi-automatic only, reflecting Auto-Ordnance Corporation's focus on reliability for military applications. During prototyping, adaptations addressed initial design limitations, including a shift from early 5-round fixed box magazines loaded via stripper clips to 20-round detachable box magazines to improve sustained fire capacity. Experiments also explored the cartridge as a means to reduce and weight while maintaining effectiveness, with prototypes tested in this configuration to evaluate performance improvements. Production of these early models by Auto-Ordnance involved limited runs, often requiring extensive hand-fitting due to tolerances and the complexity of the Blish system, which complicated efforts. Internal testing by Auto-Ordnance preceded formal military evaluation, culminating in the submission of the 1923 model to the U.S. Army Ordnance Department in 1924 for comprehensive trials at facilities like . These trials assessed key attributes such as accuracy at various ranges, reliability under repeated cycling (including dependence on lubricated ammunition), and endurance through prolonged firing sequences, where the rifle demonstrated challenges like high bolt velocities and extraction pressures but provided valuable data on feasibility.

Evaluation and Rejection

In the late 1920s, the U.S. Army conducted trials to evaluate potential replacements for the bolt-action rifle, with the Thompson Autorifle Model 1929 chambered in emerging as a key contender alongside John D. Pedersen's delayed-blowback design and early gas-operated prototypes by John C. Garand. These trials, peaking between 1927 and 1929 at facilities like , focused on reliability, ease of maintenance, and performance under simulated field conditions using the lighter cartridge to reduce and compared to the standard .30-06. The Autorifle's retarded-blowback mechanism, reliant on the principle of metallic adhesion, was tested against competitors emphasizing simpler gas or primer actuation systems. Specific criticisms during these evaluations centered on the Autorifle's operational demands and mechanical shortcomings. The Blish Lock system, intended to delay bolt opening through surface friction, paradoxically required lubricated ammunition to mitigate excessive extraction pressures in rifle calibers, rendering it impractical for troops in dusty or muddy environments where dry or fouled rounds could cause failures to feed or extract. Additionally, the violent ejection of spent cases—reportedly powerful enough to embed brass into wooden backstops during 1924 preliminary tests—posed safety risks to nearby personnel and contributed to occasional jams when casings ricocheted or interfered with the action. High production costs, stemming from the rifle's intricate machined components and the need for specialized lubricated .276 Pedersen rounds, further diminished its viability amid the Army's budget constraints post-World War I. The 1929 trials exposed significant reliability issues under field-like conditions, including inconsistent cycling and feeding from stripper clips, culminating in the catastrophic failure of the rifle's bolt after just 1,106 rounds in an endurance test. Although earlier inconclusive comparisons, such as the 1927 matchup against Garand's M1924, kept the Autorifle in contention briefly, it was ultimately withdrawn as unsatisfactory by 1930, paving the way for Garand's design to prevail in subsequent 1932 evaluations leading to the M1's adoption. Internationally, the Autorifle garnered brief interest, with samples offered for British Army trials in the mid-1920s, but no foreign militaries adopted it due to these persistent mechanical flaws.

Design and Operation

Operating Mechanism

The Thompson Autorifle employs a delayed blowback operating mechanism centered on the principle, a friction-based system designed to retard the bolt's rearward movement until chamber pressure has sufficiently decreased. Developed by U.S. Navy Commander John Blish, this mechanism relies on the interaction of angled surfaces between the bolt and barrel extension, where high gas pressure generates frictional resistance to prevent premature unlocking, allowing the rifle to safely handle high-pressure cartridges like the . Unlike traditional locked-breech designs that use mechanical interlocks, the Blish Lock achieves delay through the adhesion of dissimilar or inclined metal surfaces under pressure, with the friction diminishing as pressure falls to a safe level, such as below 500 pounds per square inch. In practice, the Autorifle's implementation features an or steep-threaded arrangement on the bolt face that engages the barrel extension, creating oblique contact points that exploit this pressure-induced for temporary locking. The cycle of operation is strictly semi-automatic, initiating when the trigger releases the bolt from its forward, cocked position. The , carried in the bolt, strikes the primer of the chambered round, igniting the and generating gas that propels the down the barrel. During this phase, the Blish Lock's angled surfaces—typically inclined at around 71 degrees to the barrel axis—clamp the bolt firmly to the barrel extension, resisting rearward force until the exits and drops. Once the critical low is reached, releases, allowing the bolt to accelerate rearward under residual gas impulse, extracting and violently ejecting the spent cartridge case via a fixed or pivoting ejector. The recoil spring then drives the bolt forward, stripping a new round from the detachable box magazine and chambering it, while the bolt rotates slightly to re-engage the interrupted threads for the next cycle. A manual safety prevents unintended firing, and the system lacks selective-fire capability in standard Auto-Ordnance models, relying instead on the bolt's interrupted for secure closure when not in operation. This delayed blowback approach distinguishes the Autorifle from simple blowback systems, which depend solely on bolt mass and recoil spring tension to control high-pressure rounds and often require heavier components or lower-powered . By introducing a pressure-dependent delay without full mechanical locking, the Blish system enables the use of potent .30-06 cartridges in a lighter semi-automatic design, though it demands precise engineering to balance and timing. A unique operational requirement is the lubrication of , typically achieved by oil-soaked pads in the that coat cartridge cases to minimize on the angled surfaces and prevent extraction failures or case ruptures during the high-pressure phase.

Specifications

The Thompson Autorifle was chambered primarily in the cartridge, with a standard of approximately 2,700 feet per second from its rifle-length barrel. Later variants, including prototypes submitted for U.S. trials in the mid-1920s, were adapted to the cartridge to reduce recoil and weight while maintaining comparable ballistic performance. Unloaded, the rifle weighed 9 pounds 10 ounces, making it lighter than many contemporary full-power battle rifles like the . It featured adjustable suitable for engagement distances up to an of around 500 yards, consistent with .30-06 ballistics in semi-automatic platforms. The Autorifle employed a semi-automatic action, allowing a practical sustained limited by the shooter's ability to aim and reload, typically 40–60 rounds per minute in controlled fire. Feeding was via detachable box magazines holding 10 or 20 rounds of .30-06 ammunition, though some prototypes included provisions for fixed magazines or loading directly into the internal magazine.
SpecificationModel 1923 (.30-06) Details
Caliber
Barrel Length24 in
Weight (unloaded)9 lb 10 oz
Magazine Capacity10 or 20 rounds (detachable box)
Muzzle Velocity~2,700 fps
Effective Range~500 yards
SightsAdjustable

Limitations and Issues

The Thompson Autorifle exhibited significant limitations stemming from its delayed blowback mechanism, particularly its reliance on the system, which compromised reliability in varied operational conditions. A key dependency was on for consistent performance; the design necessitated oiled cartridges, facilitated by oil-soaked felt pads inserted into the magazine well, as dry led to frequent failures to feed or extract. This requirement proved problematic in dusty environments, where contaminants could clog the mechanism, or in cold weather, where oil viscosity increased, exacerbating malfunctions during extended use. Ejection issues further highlighted the system's instability, with spent cases expelled at high velocities due to the rapid bolt opening once the disengaged. This violent ejection could embed brass into wooden surfaces up to 20 feet away, endangering the operator or nearby personnel, and was particularly inconsistent in prototypes where tolerances varied, leading to occasional case ruptures or jams. Manufacturing the Autorifle posed substantial challenges owing to the Blish lock's intricate design, which required precise machining of coarse threads and interlocking surfaces to achieve the intended delay in blowback. These tight tolerances elevated production costs and extended fabrication times, as forming the specialized components was labor-intensive and ill-suited for large-scale output, resulting in only limited batches for testing rather than viable commercial production. The weapon's recoil was excessively heavy for a chambered in .30-06, intensified by the lightweight recoiling parts and lack of dedicated buffer systems common in full-automatic firearms, which made sustained fire difficult to control and increased shooter fatigue. Maintenance demands added to the Autorifle's impracticality, as field stripping involved more steps than standard bolt-action rifles, including disassembly of the and lubrication components, while the delayed blowback action accumulated carbon fouling in the bolt face and receiver, requiring regular and thorough cleaning to prevent binding or extraction failures.

Variants

Auto-Ordnance Models

The Auto-Ordnance models of the Thompson Autorifle encompassed the primary domestic production variants developed and manufactured by the Auto-Ordnance Corporation in New York. These semi-automatic rifles retained the core Blish Lock delayed-blowback mechanism but were produced in extremely limited quantities solely for evaluation purposes, with no commercial sales or widespread adoption. Total output across all models remained under 50 units, reflecting the experimental nature of the project and lack of military interest. The Model 1923, chambered in , marked the initial production effort and was contracted to Colt Firearms for assembly. Twenty units were manufactured between 1923 and 1924, equipped with basic semi-automatic functionality and detachable box . Active from 1923 to 1925, these rifles featured standard and wooden stocks without significant ergonomic enhancements. No provisions for full-automatic fire were included, maintaining a focus on controlled semi-automatic operation. Variants of the Model 1923 included a configuration with a fixed internal and a heavy-barreled version with a bipod. Subsequent development led to the Model 1929, an upgraded iteration chambered in the cartridge to address reliability concerns with higher-pressure ammunition. A small number of prototypes were built by Auto-Ordnance and tested in U.S. Army trials in , incorporating modifications such as improved sights for better accuracy and refined stocks for enhanced handling. Like its predecessor, the Model 1929 omitted full-automatic capability, prioritizing semi-automatic performance in a lightweight configuration. These efforts represented the final substantive U.S. production phase before the Autorifle concept was abandoned.

BSA Autorifle

In 1926, Birmingham Small Arms Company (BSA) acquired licensing rights from the Auto-Ordnance Corporation to produce a variant of the Thompson Autorifle for evaluation by the British military. The BSA Thompson Auto-Rifle employed the Blish principle for delayed blowback and was offered for British Army trials during the 1920s. A small number of prototypes were produced, but the design was not adopted.
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