Description
U.S. Browning M2HB .50-Caliber Machine Gun Rear-Sight Base Assembly, P/N 6528338
Item Overview
This U.S. military rear-sight base assembly was made for the flexible Browning M2 heavy-barrel .50-caliber machine gun, widely known as the “Ma Deuce.” It mounts directly to the top rear of the receiver and forms the foundation for the gun’s folding mechanical rear sight. This example is the stripped base only and does not include the sight leaf or adjustment components.
Identification and Features
Part number 6528338 identifies the later-numbered rear-sight base assembly and cross-references to NSN 1010-00-243-6555. The earlier wartime drawing number was D28338. The 1944 edition of TM 9-1225 identifies “BASE, REAR SIGHT, ASSEMBLY—D28338” in the exploded rear-sight group for M2 heavy-barrel guns. Machined mounting surfaces and openings allowed the base to attach to the receiver and support the complete folding sight mechanism.
- Official component: Base, Rear Sight, Assembly
- Part number: 6528338
- Earlier drawing number: D28338
- NSN: 1010-00-243-6555
- Caliber application: .50 caliber
- Parent weapon: Browning M2 heavy-barrel machine gun
- Configuration: Flexible ground and vehicle gun
- Installation: Top rear of receiver
- Included: Stripped rear-sight base
Historical Background
The M2HB rear-sight group was standardized as a set of separate, replaceable ordnance components. Wartime manuals listed the D28338 base with the rear-sight leaf, slide, aperture, elevating screw, windage screw, knobs, scale, springs, cover plate, and mounting hardware. The later 6528338 number continued the identity of the base within the military supply system. This numbering history connects the part to both World War II maintenance literature and later M2HB support catalogs.
Function and Operation
The base bolted to the receiver and held the folding rear-sight leaf in proper alignment with the front sight. On a complete sight, the gunner raised the leaf, moved the elevation slide for the required range, and used the windage mechanism to correct the sight line left or right. The leaf folded down against the receiver when it was not needed. Because the base controlled the position of the other sight parts, a secure and correctly aligned mounting surface was important to mechanical sight accuracy.
M2HB Weapon-System Background
The Browning .50-caliber machine gun grew from a large-caliber design developed after World War I. The Army tested the weapon in 1918, and an early version entered service as the M1921 in 1923. Continued development produced the M2 family. The M2 heavy-barrel model is an air-cooled, belt-fed, recoil-operated machine gun built for sustained ground and vehicle use. Its basic receiver design proved durable enough to remain in military service through decades of changing mounts, vehicles, and sighting equipment.
Mounting and End-Item Application
This rear-sight base belongs to the flexible M2HB configuration operated by a gunner using the weapon’s spade grips. The flexible gun could be installed on the M3 ground tripod and on compatible vehicle or pedestal mounts. Because the rear sight was attached to the receiver, it remained part of the gun when the weapon was moved between mounts. The base is a gun-mounted sight component and is not part of the tripod, vehicle socket, cradle, or pedestal.
History of Use
The M2HB served as a heavy direct-fire weapon during World War II and continued in use through Korea, Vietnam, the Gulf War, and later operations. Ground crews used tripod-mounted guns for defensive and supporting fire, while vehicle-mounted examples armed tanks, armored carriers, trucks, and other military vehicles. Its .50-caliber fire was used against personnel, equipment, light vehicles, and protected positions. The receiver-mounted mechanical sight gave the gunner a built-in aiming system when firing from these flexible ground and vehicle mounts.
Condition
This military-surplus component is a stripped rear-sight base, not a complete M2HB rear sight. The folding leaf or ladder, aperture and elevation slide, windage screw and knob, windage scale, springs, associated small parts, cover hardware, and receiver mounting screws are missing. Includes only the base shown or represented by the inventory photographs.
Ideal For
This original M2HB sight component is suitable for a display-gun restoration, replacement-parts collection, museum exhibit, or technical study of the Browning .50-caliber machine gun. Its documented part-number lineage also gives it value as an identifiable example of the M2HB’s mechanical sighting system.
- M2HB display restoration
- Military museum exhibits
- Historic machine-gun collections
- Ordnance reference collections
- Mechanical sight studies
Approx length 6", Approx width 3", Approx height 1.5", Approx weight 1.1lbs.
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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