It includes a 26-inch chrome-moly barrel, 6-groove, RH 1:10-inch twist, and 48 inches overall length.
The receiver is modified in octagonal form, drilled, and slotted for a scope rail.
The scope rail is mil-standard with boss to engage cross-slot on the receiver.
The buttplate is vertically adjustable, specifically built for heavy calibers.
ArmaLite announced the introduction of the AR-31 at the National Association of Sporting Goods Wholesalers Expo in October 2013.