‘Each water-jacket contained 7.5 pints of water when full.’ This is from the early documentation of water-cooled machine guns, and it is a reminder that today’s shooters have forgotten: supporting fire was once handled as much by plumbing and buckets as by barrels and springs.
That’s an old idea that appeared in a very modern setting at the SHOT Show, where KAK Industry unveiled the LIMA 1917 Complete Water Cooled belt-fed design, which is superficially similar to John Browning’s M1917, but based on a modern belt-fed upper and an AR-platform lower. It is not a copy of the classic design’s internal workings, but rather a deliberate revival of the water jacket and condenser concept that powered the early heavy machine gun designs.
At the center is a belt-fed upper that is based on the LIMA 6 pattern and is intended for use with M27 5.56x45mm links. The mounting system is also very much modern in its practicality: the system can be mounted on a tripod via a mount that takes advantage of the unused magazine well area to provide an interface point, allowing a belt-fed upper to be used like a crew-served system without requiring a special receiver.
The hallmark of the engineering design is the water jacket itself. KAK’s water jacket is closed off by O-rings on both ends and has a capacity of 118 fl oz (3.4 liters) of water, which is admitted via a retained plug on a wire lanyard. As the barrel heats up, water boils, producing steam that rises to the top of the water jacket and then travels through a steam tube to a condensing can, where it can be recaptured and returned to the system. The design is meant to achieve the same effect as the older design on guns such as the Vickers, which used a steam condenser to reduce vapor and conserve water.
One thing that is worth mentioning is the material selection: the jacket is made of 6061 aluminum. While in firearm components, 6061 is often prized for its strength-to-weight ratio, corrosion resistance, and properties of heat movement, such as high thermal conductivity, in a water-jacketed design, this is important because the jacket serves both as a structure and a heat transfer component, rather than simply being a cosmetic component.
From a mechanical perspective, the family the system remains in is AR, where it matters. The upper features a Stoner-type direct impingement design, in which the gas is channeled to the carrier and expands within it to cycle the gun, a design that is famous for keeping the recoil in-line with the barrel and for not stressing the receiver. This type of design can be described as follows: the gas is channeled into the carrier so that it can expand between the bolt and bolt carrier as opposed to hitting a piston head.
The configuration specifications emphasize that this is a functional build, and not a mere display model throwback. The barrel is 18 inches with a heavy profile, mid-length gas system, .875-inch gas block, and 1/2×28 muzzle thread for standard muzzle devices. The action necessitates a rotated gas tube location, which is a reflection of the practicalities of fitting a belt-fed feed path and operating components into an AR-sized package. The front of the barrel features a fixed front sight for co-witnessing with a rear sight and optics.
The lower receiver requirement is simple: a lower and a buffer tube. After that, the kit is said to be compatible with legal lower configurations, such as registered receivers and other controlled configurations, and the discussion remains focused on how enthusiasts configure their belt-fed firearms.
Water cooling never went out of style as a concept; it just became inconvenient. The LIMA 1917 design makes it convenient again by considering the jacket, steam tube, and condenser as a whole system then wrapping it around a modern belt-fed action that already speaks AR.
