Mk266 Mod 1 HEI-T round

Also known as

Mk266 HEI-T
Mk 266 HEI-T
Mk266 Mod 1 HEI-T
30x173mm Mk266 HEI-T
30 mm x 173 Mk266 HEI-T

Northrop Grumman's Mk266 Mod 1 HEI-T is a U.S.-origin 30x173mm high-explosive incendiary tracer round for Mk44 Bushmaster chain guns and other 30x173mm cannons. Army and Navy ammunition documents describe it as a low-drag, tracer-equipped cartridge fielded in shipboard gun systems.

Mk266 Mod 1 HEI-T round, 30 mm high explosive incendiary tracer round, Munitions

Image source: 30x173mm Bushmaster Chain Guns

Profile / Specs

Profile

Origin: United States
Built by: Northrop Grumman
Type: 30 mm high explosive incendiary tracer round
Service note: 2010s-present
Unit cost: About $125 per round (FY 2017 Army procurement request: $6.000 million for 0.048 million cartridges)
Produced: 2010s-present
Developed from: PGU-13 HEI round

ammunition autocannon high explosive incendiary tracer

Specifications

Caliber: 30x173 mm
Designation: Mk266 Mod 1 HEI-T
Cartridge weight: About 655 g
Projectile weight: About 362 g
Muzzle velocity: About 3,540 ft/s (1,079 m/s)
Tracer burn time: At least 4.7 s
Fuze: Low-drag

Firing Weapons

Northrop Grumman and Army ammunition documents place Mk266 Mod 1 HEI-T in the 30x173mm Bushmaster family and in shipboard gun service.

Firing weapon

Weapon type

Firing evidence

DS30M 30 mm naval gun, Naval gun, Naval Systems

DS30M 30 mm naval gun

30 mm naval gun mount

The DS30M family uses the Mk 44 cannon, and the Mk266 HEI-T is described as a 30x173mm round usable in Mk44 or other 30x173mm cannons.

Sources: MK 266 Mod 1 HEI-T - PEO Ammunition, MSI-DS SEAHAWK DS A2

Service And Conflict Use

Service History

In service: Procured for the Navy's MK46 Mod 2 Gun Weapon System on San Antonio-class LPDs and Littoral Combat Ships.
Used by: U.S. Navy

Media

Mk266 Mod 1 HEI-T round Images

Mk266 Mod 1 HEI-T round, 30 mm high explosive incendiary tracer round, Munitions - view 1 — Source: 30x173mm Bushmaster Chain Guns

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Sources

MK 266 Mod 1 HEI-T - PEO AmmunitionPublisher: PEO Ammunition / U.S. Army | Note: Supports the Mk266 Mod 1 HEI-T designation, cartridge data, tracer and fuze details, and shipboard gun context. | Accessed: 2026-06-27 FY 2017 Army Ammunition Justification BookPublisher: U.S. Army | Note: Supports the FY 2017 MK266 procurement request of $6.000 million for 0.048 million cartridges, implying about $125 per round. | Accessed: 2026-06-27 30x173mm Bushmaster Chain GunsPublisher: Northrop Grumman | Note: Supports the 30x173mm Bushmaster family context and the official product images used on this page. | Accessed: 2026-06-27 MSI-DS SEAHAWK DS A2Publisher: MSI-Defence Systems | Note: Supports the DS30M Mk 44 cannon context used in the reciprocal relationship section. | Accessed: 2026-06-27