M26 MASS (Modular Accessory Shotgun System)

Published on April 22, 2026
Duration: 10:30

The M26 MASS is a bolt-action, 12-gauge underbarrel shotgun system adopted by the US military in 2012. Manufactured by Seymour Products, it was designed to be modular and attach to the M4 carbine, offering capabilities from door breaching to CQB operations. It utilizes box magazines and features a reversible charging handle and folding iron sights for compatibility with the M4.

Quick Summary

The M26 MASS (Modular Accessory Shotgun System) is a bolt-action, 12-gauge shotgun adopted by the US military in 2012, manufactured by Seymour Products. It attaches under an M4 carbine's barrel, offering capabilities for door breaching, riot control, and CQB. It fires various 12-gauge rounds from 3 or 5-round box magazines.

Chapters

  1. 00:04Introduction to M26 MASS
  2. 00:14What is the M26 MASS?
  3. 00:33Manufacturer: Seymour Products
  4. 00:48Development History
  5. 01:15Concept: Modular Shotgun System
  6. 01:31Comparison to Master Key
  7. 01:50Core System: Bolt-Action
  8. 01:55Magazine Feed System
  9. 02:00Ammunition Types
  10. 02:23Operational Uses
  11. 02:47Reversible Charging Handle
  12. 02:57Magazine Capacities
  13. 03:11Gauge and Shell Lengths
  14. 03:25Magazine Operation
  15. 03:35Cycling the Action
  16. 03:56Manual Safety
  17. 04:04Iron Sights
  18. 04:17Folding Sights
  19. 04:51Mounting on M4 Handguard
  20. 05:05Front Mounting Block
  21. 05:42Breaching Muzzle Device
  22. 06:14Detachable Pistol Grip/Stock
  23. 07:01Quick Disassembly
  24. 07:10Bolt Handle Removal
  25. 07:50Bolt Assembly Removal
  26. 07:53Internal Mechanism: Hammer-Fired
  27. 08:15Locking Mechanism
  28. 09:18Cartridge Feeding Mechanism
  29. 09:49Conclusion and Availability

Frequently Asked Questions

What is the M26 MASS and who manufactured it?

The M26 MASS (Modular Accessory Shotgun System) is a bolt-action, 12-gauge shotgun designed to be attached under the barrel of an M4 carbine. It was adopted by the US military in 2012 and is manufactured by Seymour Products, a company primarily known for optics.

What types of ammunition can the M26 MASS fire?

The M26 MASS can fire a variety of 12-gauge ammunition, including birdshot (#7.5 and #9), a specialized breaching slug made of powdered metal, rubber slugs and buckshot, and standard double buckshot. It accepts both 2.75-inch and 3-inch shells.

How does the M26 MASS attach to an M4 carbine?

The M26 MASS replaces the bottom handguard of an M4 carbine directly, fitting around the barrel. A mounting block at the front secures it to the M4's front sight assembly, allowing for a modular integration without special brackets.

What are the operational uses for the M26 MASS?

The M26 MASS is designed for multiple roles including door breaching, riot control, and close-quarters combat (CQB) operations. Its modularity allows soldiers to carry a shotgun capability without a separate firearm.

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