The FAS-173 was designed by John Foote, who based it on an assault rifle he had built based on the AK series.
The FAS-173 is gas-operated, utilizing a long-stroke piston gas system. It is almost built entirely of steel, while prototype 20 gauge versions have steel-lined aluminum barrels. It uses a gas system similar to that on an AK-styled rifle. The weapon has a wood stock, though plastic stocks and side-folding stocks are also available. While the weapon's designation is similar to the FAC-70 which Foote himself also designed, the weapon resembles the older R68 much more.