Atrius Development X-Series Ambidextrous Forced Reset Selector

The Atrius X-Series is the gas-piston Forced Reset Selector. It is an ambidextrous selector with a new trip system: a trip base and a trip clutch, built so the reset path can fit SIG piston guns whose carriers do not present the trip surface an AR-15 bolt carrier does.

Atrius launched it for MCX, MCX-Spear LT, MCX-Rattler LT, Sig's MCX-Spear LT Upper AR Conversion Kit, MPX PCC, MPX-K, and MPX Copperhead. That host list does not include the full-size .308 or .277 FURY Spear, and it does not cover every SIG piston gun. The comparison table on the product page marks FRS Ambi X-Series as the only current Atrius row for gas-piston systems. G-Lever stays the Geissele and reduced-hammer path; X-Series has no lever blocker.

The selector uses the original Atrius ambi lever design with a new FRS lever dimensioned for MCX and MPX product lines. Configuration is Safe, Semi, and Super-Semi. Construction is heat-treated 4140 steel with a corrosion-resistant black nitride finish, made in the USA. Atrius calls the install drop-in with no modifications and no trigger cutting. After the selector and fire control group go in, the trip base seats on the left side of the receiver against the rear trigger pin, the trip clutch rides the trip-base track, and the trip base tucks under the rear takedown pin before a dry function check.

Standard Atrius trigger caveats still apply: mil-spec triggers without a U-notch or relief cut, cassette and drop-in compatibility that varies, and G-Lever as the Geissele path. The Atrius product page also quotes an ETA lead time of 3-4 weeks, a chrome note that it ships within 2 business days, a 5-unit purchase cap, and a restricted-state list that includes California, New York, Illinois, Florida, Virginia, Washington, US territories, and international destinations. Check that page before you order.