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M3A1 (Grease Gun) Suppressed

Submachine Gun (SMG) [ 1944 ]

The suppressed M3A1 was a wartime OSS attempt at a special-use M3A1 Grease Gun submachine gun.

Authored By: Staff Writer | Last Edited: 12/15/2017 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site.

Designed in 1942 with serial production beginning in 1943, the original M3/M3A1 "Grease Gun" submachine gun (SMG) series was procured at the unbelievably low price of $20 per unit in 1943 dollars. The weapon was commissioned from the outset as a budget-conscious, mass-production effort to supplant the more complex and expensive (though still excellent) M1 Thompson SMG series. The Grease Gun was produced to the tune of some 700,000 examples over its service life and managed an active existence extending into the 1990s. It was eventually used throughout the world and across several notable conflicts proving the design sound and something of a market success. The M3 eventually was slightly improved through the M3A1 initiative and chambered for both the American .45 ACP and German 9x19mm Parabellum pistol cartridges, these firing through a blowback, open-bolt action (most production was of the .45 ACP form however). The weapon began appearing in useful numbers from late-1944 into 1945 though saw more widespread use only after the war.

The "Grease Gun" name was derived from the weapon's appearance to a mechanic's grease gun of the period. The original weapon was designed by George Hyde of General Motor's Inland Division with production handled by General Motor's Guide Lamp Division of Indiana.

During the war, the Office of Strategic Services - forerunner to the Central Intelligence Agency of today - entertained the thought of a suppressed version of the weapon. This revision retained the basic form and function of the reworked M3A1 while adding an integral suppressed barrel to the design. The barrels were drilled in specific areas for dispelling propellant gasses and attached to the receiver via specially-designed nuts. Design of the suppressor was attributed to Bell Laboratories at the request of the OSS while barrels were manufactured by Guide Lamp Division with final assembly by the High Standard Firearms Company. ©MilitaryFactory.com
The weapon was not truly a "silent" weapon for it still managed the standard, low-velocity .45 ACP cartridge - inherently subsonic but still producing a telltale sound. The suppressor aided some in retarding the operator's sound profile but the combination was not efficient. The remainder of the gun was largely unchanged and included the standalone pistol grip, collapsing twin-strut wire buttstock, tubular receiver and 30-round straight box detachable magazine which doubled as the forward grip. .

The OSS commissioned for some 1,000 suppressed M3A1s which certainly limited their overall reach in World War 2. Their suppression qualities proved poorer than the excellently-suppressed competing British STEN submachine guns - some 20% more audible than the British design.©MilitaryFactory.com
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Service Year

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United States


Submachine Gun (SMG)

High Standard Firearms Company - USA
(View other Arms-Related Manufacturers)
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(OPERATORS list includes past, present, and future operators when applicable)
This weapon is either inherently silent/suppressed or can be made so through special assembly added at the muzzle, specialized subsonic ammunition or a combination of both.

Overall Length
762 mm
30.00 in
Barrel Length
203 mm
7.99 in
Empty Wgt
8.16 lb
3.70 kg

Iron Front and Rear


Blowback; Open Bolt

Blowback Operation
Gas pressure from the rearward movement of the ignited cartridge case provides the needed bolt movement, ejecting the spent case and stripping a fresh case from the magazine.
Open Bolt
System utilizes internal mechanism where bolt and associated working components are set to the rear of the receiver with no cartridge chambered; trigger actuation moves bolt forward, chambers cartridge, and fires bullet in single action - ultimately resetting during the complete cycle by way of the generated energy.
(Material presented above is for historical and entertainment value and should not be construed as usable for hardware restoration, maintenance, or general operation - always consult official manufacturer sources for such information)


.45 ACP

Rounds / Feed

30-round detachable box magazine
Cartridge relative size chart
*May not represent an exhuastive list; calibers are model-specific dependent, always consult official manufacturer sources.
**Graphics not to actual size; not all cartridges may be represented visually; graphics intended for general reference only.
Max Eff.Range
250 ft
(76 m | 83 yd)
Muzzle Velocity
900 ft/sec
(274 m/sec)

M3 - Base series designation; initial production model.
M3A1 - Improved M3 submachine gun

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