Copyright International Ammunition Association, 2007. All rights reserved.
Cartridge of the Month June 2007

Stinger-37 Stun Bag by MBAssociates
Specimen, description and and photos courtesy of Mel Carpenter
Sectioning done by Paul Smith

In 1969, MBAssociates (MBA) Ordnance Systems Manager, Robert Mawhinney began work on a less-lethal option for law enforcement personnel. The first step was to review what little work in the field had already been done, mainly with ideas that were tried by others and discarded.

On May 4th, 1970, four students were killed and nine were injured at Kent State University by Ohio National Guard soldiers who had no less-lethal equipment, only .30-06 caliber rifles with M2 Ball ammunition. As a result of the incident, MBA placed a high priority of the development of a less-lethal system, initially for the military to use in existing 40mm M79 and M203 grenade launchers.

Later in 1970, Mawhinney invented the MBA Stun-Bag round, with a 3-inch diameter canvas bag containing about five ounces of #8 or #9 shot. The bag was propelled by a small amount of gunpowder based on the anticipated range required. When police and corrections personnel asked for a similar product that could be used with their 37mm tear gas guns, MBA reduced the round’s size to 37mm, or 1.5 inches, and designed the Stinger-37 rifled adapter to be attached to the muzzle of the tear gas gun to spin the bag so it would hit it’s target flat.

The 37mm version is shown here, with the sectioned round done by Paul Smith. It used the same basic high-low pressure design of the 40mm M79/M203 series of grenade cartridges where the propellant is contained in a small chamber – a copper cup in the MBA version – so it can burn properly while being contained under high pressure. The high pressure ruptures the copper cup, allowing gas to flow into the larger cartridge base where it’s pressure is reduced in order to propel the stun-bag at it’s low velocity of about 150 feet per second. The round’s primer is held in place by an aluminum bushing. The aluminum cases were manufactured for MBA by Harvey Aluminum of Torrance, California. MBA loaded the rounds at its San Ramon, California factory.


The round is 103.3mm/4.06 inches long, the rim is 43.4mm/1.71 inches, and the straight case is 38mm/1.5 inches.


There were several versions of  Stinger-37 ammunition:

1- Close-Range, 3 grains of powder;
2- Low-Impact, 3.3 grains;
3- Standard, 3.8 grains;
4- Long-Range, 4.1 grains;
5- Super Long-Range, 4.5 grains;
6- Duplex, 4.5 grains and two 2.5-inch bags;
7- Triplex, 4.5 grains and three 2-inch bags;
8- Loose plastic shot;
9- Multi-Baton with 5 wood blocks; and
10- CS/CN/Smoke rounds.

All of the stun-bag rounds were available with a bright yellow marking dye.


The reloadable but expensive – one standard round cost $10.60 in 1972 – cartridges were later modified to use a .38 S&W blank and with different case designs. But that’s another story. All of MBA’s less-lethal ammunition and devices will be covered in Mel Carpenter’s book to be completed this year. 



Mel is continuing his research and would love to hear from anyone who has MBA gyrojet firearms or cartridges, factory literature, or any other information about MBA gyrojets and other MBA ordnance products . Contact Mel Carpenter


Copyright 2007 by the International Ammunition Association, Inc. All rights reserved.

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  Revised 2 June 2007