AS Designs MCX Heavy Slip Trip Kit (.308 / .277 FURY)

The AS Designs MCX Heavy Slip Trip Kit is the part that makes a forced reset selector work on the heavy-caliber SIG MCX Spear, the .308 Winchester and .277 SIG FURY guns. It is not a trigger and not a selector by itself. It pairs with an AS Designs Arc-Fire V2 selector, supplying the reset trip that system needs on the Spear carrier. A standard AR bolt carrier presents a trip surface the forced reset mechanism rides against; the heavy MCX carrier does not, so without this kit an Arc-Fire cannot reset the trigger on a Spear.

The kit ships with a 4140 steel slip trip in black oxide, a 7075-T6 aluminum slip trip guide, and a transfer lever cut specifically for the SIG Spear in .277 FURY and .308. That dedicated transfer lever is why the heavy kit exists as a separate part from the standard MCX slip trip: the heavy-caliber Spear action needs its own reset geometry. You buy the selector separately.

Fitment is caliber-specific. The kit runs on the MCX Spear in .308 and .277 FURY across all generations, though early-generation guns may need the factory safety latch removed. It works with the Arc-Fire V2 and with Geissele triggers modified for Arc-Fire use. It is not compatible with the AR Super Safety, the Atrius Super Selektor, factory Timney triggers, or cassette and traditional forced reset triggers, and it does not fit the MCX in .223, .300 BLK, or 7.62x39, or the MPX. Some hand-fitting is normal, and a qualified gunsmith is recommended. Confirm your Spear caliber and generation, and current state law, before ordering.