They claimed it was not a “new and improved” AR, but a patented revolutionary gas piston system with other key features that set it apart from all other M4-type rifles.

[4] On May 12, 2011, Adcor announced that its A-556 rifle had been entered in the U.S. Army's Individual Carbine competition.

[6] On 17 July 2013, Adcor announced it would not protest the Army's decision to terminate the program, and would focus on delivering A-556 rifles to commercial customers.

Test results made available to the company said the Army found the A-556 provided “outstanding” accuracy, even after firing thousands of rounds.

A gas-driven piston is incorporated into the upper half of the forward rail system and never touches the barrel.

The operating rod is connected to the bolt carrier group and rides through a machined boss in the receiver rail system interface, keeping the bolt carrier in a linear plane as it operates.

[7] By contrast, on weapons like the Adaptive Combat Rifle and the FN SCAR, the charging handle is raised off the side rails, allowing things to be mounted.