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Knight's Armament Company Masterkey

Door-Breaching Under-Barrel Shotgun Module [ 1985 ]

The KAC Masterkey was developed to broaden the tactical reach of the special forces operative, giving him a compact and effective door-breaching tool.

Authored By: Staff Writer | Last Edited: 02/26/2018 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site.

Door breaching has long been a technique relied upon by various law enforcement, special forces elements, and standard infantry to gain entry to otherwise inaccessible areas. Various systems have been devised over the decades to breach such obstacles as doors and, during the 1980s, the Knight's Armament Company (KAC) of the United States developed the "Masterkey" for this very purpose.

The weapon was essentially the primary working components of the classic Remington M870 pump-action shotgun and this was mounted under the forward section of a standard assault rifle such as the Colt M16. The reduced profile of the M870 reduced the amount of carried shells to four (with one shell being chambered) and, lacking any sort of stock or grip of its own, the magazine of the rifle doubled as the grip handle, providing access to the M870's trigger unit which was retained from the shotgun. The end result was an effective battlefield piece suitable for door breaching and one that added little length and weight to the rifle.

Notable operators of the Masterkey included United States Delta Force. The shotgun door-breacher concept continues today in such developments as the M26 Modular Accessory Shotgun System (MASS) produced by C-More Competition (and detailed elsewhere on this site).©MilitaryFactory.com
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Service Year

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United States


Door-Breaching Under-Barrel Shotgun Module

Knight's Armament Company (KAC) - USA
(View other Arms-Related Manufacturers)
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(OPERATORS list includes past, present, and future operators when applicable)
Close Support
Extreme close quarters use; trench-clearing; doorbuster; security.
Special Forces
Qualities of this weapon have shown its value to Special Forces elements requiring a versatile, reliable solution for the rigors of special assignments.

Overall Length
432 mm
17.01 in
Barrel Length
432 mm
17.01 in
Empty Wgt
5.73 lb
2.60 kg



Manually-Actuated Pump Action System

(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)



Sample Visuals**

Graphical image of a 12-gauge shotgun shell
Rounds / Feed

3+1 rounds (one chambered)
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.
"Masterkey" - Base Series Name; modified Remington M870 used as underslung base weapon system.

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Images Gallery

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Image of the Knight's Armament Company Masterkey
Image from official Knights Armament Company marketing material.


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