United States
30 mm (1.2") Bushmaster II Mark 46 Mod 1
40 mm (1.57") Bushmaster II
Updated 22 November 2014

The 30 mm Bushmaster II is derived from the proven 25 mm M242 Bushmaster automatic weapon.  This next-generation member of the Chain Gun® family applies the same design simplicity, positive round control, ease of maintenance and constant velocity ammunition feed of the battle-proven Bushmaster cannon.  The Mark 46 system is a navalized version of the gun used on the Advanced Amphibious Assault Vehicle (AAAV) and on the San Antonio LPD-17 class.

The larger 30 mm Bushmaster II incorporates 70 percent of the logistic parts used in the 25 mm M242 Bushmaster, offering operators low-risk, proven performance and NATO common parts supply.  The production barrel will be chrome plated for extended life.

The mounting for this weapon will be shared with the Expeditionary Fighting Vehicle (EFV) - formerly known as the Advanced Attack Amphibious Vehicle (AAAV) - being built for the US Marine Corps.

From the LPD-17 website:  "The Mk 46 30 mm gun system is a two-axis stabilized chain gun that can fire up to 250-rounds per minute.  The system uses a forward looking infrared sensor, a low light television camera, and laser range finder with a closed-loop tracking system to optimize accuracy against small, high-speed surface targets.  It can be operated locally at the gun's weapon station (turret) or fired remotely by a gunner in the ship's Combat Information Center."

This weapon can be converted to fire 40 mm rounds with a change of barrels and minor changes to the feeder assembly.  This conversion can be performed by the ship's crew.

A 15 September 2005 Alliant Techsystems (ATK) Press Release announced that ATK "will provide its proven 30/40mm Mk44 Bushmaster Cannon system to MSI Defence Systems for integration onto its DS30M Mk2 Naval Mounting.  The UK Royal Navy (RN) has ordered a total of 26 systems for the new Type 23 Frigate, with deliveries scheduled to begin in late 2006.  This is the first time ATK will provide the Bushmaster for use on a RN vessel and it extends the Bushmaster’s reach beyond armored vehicle applications to shipboard use."

These 30 mm weapons replaced the 57 mm Bofors guns planned for the USS Zumwalt DDG-1000 class.

WNUS_30mm_BushmasterII_pic.jpg

Bushmaster II
Photograph copyrighted by Alliant Techsystems

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Installing a Mark 46 Mod 1 weapon system onboard USS San Antonio (LPD-17) in November 2005
This same mounting is used on USS Freedom LCS-1 and planned for the USS Zumwalt DDG-1000 class
US Navy photograph 051026-0-0000B-001

WNUS_30mm_BushmasterII_ammo_pic.jpg

Ammunition for the Bushmaster II
Note that the 40 mm round is the same overall length as the 30 mm rounds, thus simplifying the changeover to the larger caliber
Photograph copyrighted by Alliant Techsystems

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30 mm ammunition feed system for Mark 46 Mounting on USS Freedom LCS-1
US Navy photograph 130924-N-PD773-005

WNUS_30mm_BushmasterII_EFV_cutaway_pic.jpg

Cutaway view of Mark 46 Mounting showing dual-ammunition feed system
Image copyrighted by General Dynamics ATP

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Gun Characteristics
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Designation 30 mm Bushmaster II
Ship Class Used On USN
   San Antonio LPD-17
   Freedom LCS-1
   Zumwalt DDG-1000
   EFV (Armored Fighting Vehicle for the US Marines)

Britain
   Type 23 Frigates

Date Of Design about 1997
Date In Service 2004 (planned)
Gun Weight 341 lbs. (154.6 kg)
Gun Length oa 134.05 in (3.405 m)
Bore Length N/A
Rifling Length N/A
Grooves 16
Lands N/A
Twist N/A
Chamber Volume N/A
Rate Of Fire 250 rounds per minute cyclic
Note:  Weapon may be set to fire in single shot, 5 round burst or fully automatic modes.
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Ammunition
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Type Fixed
Weight of Complete Round AP-I : 1.62 lbs. (0.735 kg)
Mark 266 Mod 1 HEI-T:  1.48 lbs. (0.670 kg)
Mark 238 Mod 1 HEI-T:  1.48 lbs. (0.670 kg)
Mark 240 SAPHEI-T:  1.46 lbs. (0.660 kg)
Mark 268 APFSDS-T:  1.60 lbs. (0.725 kg)
Projectile Types and Weights
(see Note 2)
AP-I:  0.94 lbs. (0.425 kg)
HEI-T:  0.79 lbs. (0.362 kg)
SAPHEI-T:  0.79 lbs. (0.364 kg)
APFSDS-T:  0.52 lbs. (0.235 kg)
Bursting Charge AP-I:  Solid Bullet
HEI-T:  0.12 lbs. (0.056 kg)
SAPHEI-T:  N/A
APFSDS-T:  None (solid penetrator)
Projectile Length N/A
Complete Round:  11.4 in (29 cm)
Propellant Charge AP-I:  N/A
HEI-T:  0.38 lbs. (0.153 kg)
SAPHEI-T:  0.33 lbs. (0.148 kg)
APFSDS-T:  0.39 lbs. (0.176 kg)
Cartridge 30 x 173 mm
Muzzle Velocity API:  3,225 fps (983 mps)
HEI-T:  3,543 fps (1,080 mps)
SAPHEI-T:  3,543 fps (1,080 mps)
APFSDS-T:  4,544 fps (1,385 mps)
Working Pressure API:  N/A
HEI-T:  50,000 psi (345 MPa)
SAPHEI-T:  52,200 psi (360 MPa)
APFSDS-T:  52,200 psi (360 MPa)
Approximate Barrel Life N/A
Ammunition stowage per gun
(see Note 3)
about 200 rounds
Notes:

1) This weapon fires standard 30 x 173 mm GAU-8 ammunition, using a side-stripping link developed by The Boeing Company.  It can also fire RARDEN and Oerlikon KCB (30 x 170 mm) ammunition by changing the barrel, bolt and aft feed plate.

2) The major difference between the HEI-T Mark 266 Mod 1 and Mark 238 Mod 1 is that the Mark 266 Mod 1 uses a non-self destruct fuze (NSD) while the Mark 238 Mod 1 uses a self-destruct fuze (SD).

3) The navalized Mark 46 Mod 1 mounting has a dual feed magazine with 200 rounds in each feed.

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Range
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Elevation With 0.79 lbs. (0.362 kg) HE Shell
Effective Range about 2,200 yards (2,000 m)
Nominal Min/Max Range 330 to 3,300 yards (300 to 3,000 m)
Maximum Range about 4,400 yards (4,000 m)
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Mount / Turret Data
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Designation USN Single Mount
   EFV (1):  Mark 46 Mod 0
   San Antonio (2), Freedom (2) and Zumwalt (2):  Mark 46 Mod 1
Weight  N/A
Elevation -10 / +45 degrees
Elevation Rate N/A
Train 360 degrees
Train Rate up to 60 degrees per second
Gun recoil N/A
Notes:

1) The differences between the EFV Mark 46 Mod 0 turret and the navalized Mark 46 Mod 1 turret include:

   The choice of either remote unmanned operation or local 1-man operation by a single crewman.
   Unarmored turret.
   No exterior hatches or periscopes.
   No coaxial secondary weapon.
   Higher ready-round capacity than the armor variant.
   Use of Low-Light Television (LLTV) for target acquisition.

2) This weapon uses a 1.0 HP motor @ 24 VDC to operate all moving components.

3) British ships will use the DS30M Mk2 Naval Mounting.

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Data from
"The Naval Institute Guide to World Naval Weapon Systems 1991/92" by Norman Friedman
"Jane's Ammunition Handbook:  Ninth Edition 2000-2001" edited by Terry J. Gander and Charles Q. Cutshaw
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"EFV 30mm Ammunition Feed System" by Ms. Kim Perkins, General Dynamics ATP, presented at the NDIA Joint Armaments Conference, Exhibition & Firing Demonstration, May 2010
"Gun / Ammunition Acquisition Strategy for the EFV Program" by Major Ian McDuffie, USMC, presented at the NDIA Joint Armaments Conference, Exhibition & Firing Demonstration, May 2010
"Super 40mm to 30mm Ammunition Comparison – Performance/Lethality" by Mr. Rick Wright, General Dynamic, presented at the NDIA Joint Armaments Conference, Exhibition & Firing Demonstration, May 2010
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Boeing Company Press Releases
LPD-17 Design Team
US Marines EFV Website
Alliant Techsystems (ATK)
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USNI News:  "Navy Swaps Out Anti-Swarm Boat Guns on DDG-1000s" by Sam LaGrone
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Special help from Leo Fischer
Page History

11 April 2007 - Benchmark
03 June 2010 - Added data about dual-feed system, other ammunition notes, links to papers presented at NDIA Joint Armament Conference
22 November 2014 - Added notes regarding use on DDG-1000