I’m guessing it was the ADCOR. It seems to be the only one with a unique design. The newer “green” ammo seems to be a hotter round that might not do as well with the more conventional rifles.
In early 2010, Adcor sent the ADCOR A-556 rifle to H.P. White Laboratory, known for small arms and ammunition research, development, and testing, to test the reliability of the design. Testing took place from March to April. 6,000 rounds were fired in 120 round cycles, and the guns were lubricated and allowed to cool after 600 round intervals. During the tests, no parts had to be replaced and there were no jams, stoppages, or malfunctions of any kind. Following this, the A-556 was able to shoot a .88 MOA group at 100 yards with 69-grain match ammo.
http://en.wikipedia.org/wiki/Brown_Enhanced_Automatic_Rifle
Thanks. Checking it out now.