Picatinny Arsenal took a look at the M249 and experimented with reducing its hefty weight of 17.5 lbs down to 9.2 lbs. They also gave it a new name: Cased Telescoped Light Machine Gun, or CT LMG.

To achieve this impressive weight loss, they did not use exotic materials. Rather they removed material where they could and detaching the firing chamber from the barrel. Having an external firing chamber reduces the heat so the gun runs cooler and prevents rounds from cooking off.

They also went with plastic like casings for the ammunition to reduce the weight of the ammo down by 39%.