Description
Inert 20mm M1/M2 Autocannon Sear Buffer Spring in Original 1952 Package
Item Overview
This original U.S. military sear buffer spring was made for the 20mm Automatic Gun M1 and the closely related M2, later designated the AN-M2 aircraft automatic gun. The spring remains in its original Wallace Barnes Company package dated January 1, 1952. It is a small but important part of the gun’s sear block group. This mechanical component is completely inert and contains no explosive, propellant, primer, or other energetic material.
Identification and Package Markings
The printed package provides valuable identification and supply information. It names the part as a spring for the sear buffer and connects it with military drawing A-25601. The package contains one spring and identifies Wallace Barnes Company of Bristol, Connecticut, as the manufacturer. These markings make the package an important part of the item’s history and collector value.
- Item: Spring, Sear Buffer
- Application: 20mm Automatic Gun M1 and M2/AN-M2
- Package stock number: J-941-S-12838-60
- Quantity marked: 1 Each
- Drawing number: A-25601
- Manufacturer: Wallace Barnes Company
- Manufacturer location: Bristol, Connecticut
- Contract number: DA-30-144-ORD-1433
- Package date: January 1, 1952
- Status: Inert mechanical spare part
Original Service Function
The M1 and AN-M2 sear block used two sear buffer springs with plungers and supporting blocks. When the sear caught the breechblock in the cocked position, these springs absorbed part of the impact. This cushioning action helped protect the sear and related parts during repeated operation. The springs were supported at the front by steel and fiber buffer blocks. The 1942 Army maintenance manual lists a normal free length of approximately 1.89 inches for each sear buffer spring and called for replacement when the free length fell below 1.87 inches.
Sear Block and Firing System
The sear held the breechblock in its cocked position by engaging a recess in the bottom of the breechblock lock. When the firing system moved the sear out of engagement, the breechblock could travel forward and begin the firing cycle. Aircraft installations normally used an electric solenoid connected to the sear mechanism. This listing is for one sear buffer spring only. It is not the sear spring, driving spring, recoil spring, large rear buffer spring, or a complete sear block assembly.
20mm M1 and AN-M2 Autocannon History
The M1 and M2 belonged to the American 20x110mm Hispano-pattern cannon family developed for military aircraft during World War II. The Army later changed the M2 designation to AN-M2, with “AN” identifying equipment standardized for Army and Navy aviation use. Period manuals state that the M2 and AN-M2 were the same model. The M1 and AN-M2 had minor receiver differences, but their tubes and working parts were generally alike. Both were air-cooled weapons that combined gas operation with blowback action.
- Caliber: 20mm
- Ammunition family: 20x110mm Hispano
- Operating system: Gas and blowback operated
- Cooling: Air cooled
- Cyclic rate: Approximately 600 to 700 rounds per minute
- Period muzzle velocity: Approximately 2,850 feet per second
- Original mounting types: Aircraft wing, fuselage, and propeller-hub installations
- Feed systems: Magazine or mechanical feed, depending on installation
Aircraft and Service Use
The U.S. 20mm Hispano-pattern cannon family armed several important World War II aircraft. Applications included the nose-mounted cannon of the P-38 Lightning, the four-cannon battery of the P-61 Black Widow, the four wing-mounted cannons of the F4U-1C Corsair, and the wing cannons carried by later SB2C Helldiver variants. Aircraft equipped with these guns served in the Pacific, European, Mediterranean, and China-Burma-India theaters. The cannon provided greater projectile weight and destructive effect than rifle-caliber aircraft guns, making it useful against aircraft, vehicles, and other targets.
1952 Military Supply Context
The January 1952 packing date places this spring in the Korean War era, several years after the end of World War II. It should not be described as a Korean War combat-used part without additional records, but its dated package shows that the U.S. military was still maintaining replacement stocks for the M1/M2 gun family. Older aircraft cannons and related designs could remain in storage, training service, overhaul programs, or the military supply system long after newer weapons entered production.
Wallace Barnes Company
Wallace Barnes Company was part of Bristol, Connecticut’s long precision-spring manufacturing tradition. The business developed from a spring-making operation established during the nineteenth century and became known for producing specialized springs and metal components. The company name and Bristol address on this package connect the part with an American manufacturer that supplied precision components for industrial, aircraft, and military equipment.
Condition and Included Components
This listing includes one inert sear buffer spring in its original dated military package. The package may show staining, fading, wrinkles, tears, writing, softened adhesive, or other storage wear. The spring may have protective oil, dried preservative, discoloration, or light oxidation from age. It has not been tested or certified for installation in a working firearm or autocannon and is offered as a collectible military spare part. No sear, plunger, buffer block, gun, ammunition, tools, or other components are included. Please check the pictures for the general condition of the item.
Ideal For
This original packaged spring is well suited for collections and exhibits focused on military aircraft armament, American wartime manufacturing, historic gun parts, and U.S. Ordnance Department supply equipment.
- 20mm M1 and AN-M2 autocannon collections
- World War II aircraft-armament displays
- Korean War-era supply collections
- P-38, P-61, F4U, and SB2C exhibits
- Original packaged military-parts collections
- Museums, educational exhibits, and restoration-reference displays
Approx length 1.89", Approx width .36", Approx height .36", Approx weight less than .1 lbs.
Pictures are stock images of our inventory. Unless otherwise noted, you will not be receiving the exact item shown in the pictures. The pictures are representative of the item’s general condition. The item you receive might be slightly better, or worse, condition than was shown in the pictures.
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