The video below shows both a live fire demo and a lab demo of the LSAT lightweight SAW.
The video below is from Military.com. It shows the only publicly available video of the field testing at Ft. Benning according to them.
According to the article in the Kitup blog at Military.com, development of the lightweight M-249 SAW-like weapon is almost finished. It fires lightweight cased telescoped (CT) ammo. Researchers have fired about 10,000 rounds through three prototype weapons. According to Kori Phillips, the program manager,
With millions of dollars in Army research investment, the JSSAP office says it will be ready to put weapons in warfighters' hands by next year. Phillips said eight new SAWs will be built by AAI Corporation. She also said that the office plans to run an exercise with an infantry squad equipped with the new lightweight machine gun and 100,000 rounds of cased telescoped ammo.While the new weapon looks much like the older M-249 SAW it "uses a rotating action and a novel feed system that fires a standard 5.56mm ball projectile and ejects the plastic case and link from its own port." The engineers report that have completely avoided failures to feed and eject.
While the cased telescoped ammo is almost ready for actual use, there are still developmental problems with the caseless ammo.
While the cased telescoped ammo is almost ready for prime time, the more exotic caseless rounds still need some work, Phillips explained. Testers are having problems keeping the rounds -- which are essentially hard, molded propellant with an embedded 5.56 mm bullet -- from degrading in high heat. They're also expensive, hard to make, and tough on the shooter.....Excessive smoke, inexact timing and other uncertainties have kept the weapon attached to a bench.
Another article at Military.com goes into more detail about the M-4 version as well. It is interesting to read the comments regarding the lightweight ammo. One commenter noted that if the weight of ammo is cut in half he would end up just carrying twice as much.