Frankenstein Armory TSB-Heavy

The Frankenstein Armory TSB-Heavy is the part that lets you run an actual forced reset trigger, not a selector, in a heavy-caliber SIG MCX Spear in .308 Winchester or .277 SIG FURY. It is the FRT-trigger counterpart to the AS Designs Heavy slip trip: where the AS Designs kit adapts an Arc-Fire V2 selector to the Spear, the TSB adapts a locking-bar-style FRT trigger to it. The heavy Spear carrier does not present the reset trip surface an AR fire control group rides against, so the TSB supplies the surface the trigger's locking bar works against.

It is machined from 17-4PH stainless steel heat treated to the H900 condition, then tumbled to a uniform finish. Installation is drop-in: two quarter-inch stainless coil pins ship in the kit and no cutting is required. You supply the locking-bar FRT trigger separately.

Fitment covers the SIG Spear (heavy) in .308 and .277 FURY. It is explicitly not compatible with a Super Safety, so this is the block you choose when you want an FRT trigger on the heavy Spear rather than a forced-reset selector. Confirm your Spear caliber and current state law before ordering; Frankenstein Armory sells the TSB direct, and all sales are final.