Ultimax 100 Light Machine Gun


In the late 1970s James Sullivan, one of ArmaLite’s former chief designers and one of the men responsible for the M16, began developing a new light machine gun for a company in Singapore. The Ultimax 100 is a 5.56x45mm, gas-operated magazine-fed light machine gun. It uses a short stroke gas piston system that acts on a continuously recoiling bolt.

Sullivan was originally approached to develop a new select-fire intermediate cartridge rifle for the Singaporean military. Working with Chartered Industries he developed a very lightweight light machine gun. Sullivan was especially interested in recoil mitigation and developed the Ultimax’s bolt to travel rearward without ever hitting a buffer or the receiver. This greatly lowers perceived recoil and makes the weapon much flatter shooting.

Ultimax MKII
A MkII Ultimax which featured a fixed barrel (source)

The Ultimax fires from an open bolt (which uses a multi-lug rotating bolt head) and has a non-reciprocating charging handle. It’s buttstock can be removed to make the weapon even more compact. The absence of a buffer in the butt allows the weapon length to be reduced to just 81cm (32 inches), making it an excellent weapon for jungle or urban combat. The Ultimax is also extremely light for a squad automatic weapon, weighing approximately 4.7kg unloaded, and around 6.5kg when loaded with a 100-round drum.

Diagram from an early marketing brochure showing the MkII and MkIII models of the Ultimax (source)

While the MkII Ultimax has a fixed barrel, the MkIII has a quick change barrel which releases by pulling a catch the the rear and simply twisting the barrel and pulling it forward. Unlike other machine guns the bolt can remain forward when the barrel is being removed.

The Ultimax feeds from either an adapted STANAG magazine or a 100 round drum magazine, which has a controlled internal feed rather than a belt. The drum was co-developed by Sullivan and Bob Waterfield. The weapon’s rear pistol grip is similar to the Stoner 63 weapon system’s (which Sullivan had also worked on) while the smaller, grooved front pistol grip is reminiscent of the classic Thompson submachine gun’s.

Ultimax 100 Sales Brochure cover
Cover of Chartered Industries sales brochure for the Ultimax 100, featuring a MkIII, note the bayonet lug (source)

It is said that Singapore’s government would not allow the Ultimax to be entered in the US’ Squad Automatic Weapon trials as the US government had refused them the technical package for the M16. Other sources suggest there was a commercial disagreement between Colt and Chartered Industries Over region sales of the M16. As a result the FN Minimi won the trials and was adopted as the M249. Those who have fired both claim that the Ultimax would have given the Minimi more than a run for its money.  Despite this the Ultimax has seen action around the world and has been in service with the Singapore Army since 1982.

An updated version was offered in the US Marine Corps’ Infantry Automatic Rifle trial but was beaten by Heckler & Koch’s HK416, now the M27. ST Kinetics, formerly Chartered Industries, continues to improve and produce the Ultimax with the Mk8 introduced in 2012.

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Technical Specifications (from 1982 Sales Brochure):

Length: 103cm (40 in)
Weight (unloaded): 4.7kg (10.4 lbs)
Barrel Length: 50.8cm (20.0 in)
Action: Gas operated
Calibre: 5.56x45mm
Feed: 100-round drum or 30-round STANAG magazines
Cyclic Rate: ~400-600 rpm


The Interview: L. James Sullivan, Part II, 28th February 2007, Small Arms Review, (source)

1982 Ultimax 100 Sales Brochure, Chartered Industries of Singapore, (source)

The Past is Another Country: Ultimax 100, WeaponsMan, (source)

Military Small Arms of the 20th Century, I. V. Hogg, (1985)