SIG MCX-R Regulator 16" 5.56

The SIG MCX-R Regulator is SIG's purpose-built ban-state MCX. It pairs the standard MCX gas-piston upper with a redesigned lower that accepts a Magpul SGA Mossberg 500/590 shotgun-pattern stock, eliminating the pistol grip and the folding/telescoping AR-style buttstock that PICA and California catch. Every other MCX feature carries over: short-stroke piston operation, AR-15 magazine compatibility with a 10-round polymer magazine in the box, full ambi controls (safety selector, mag release, bolt catch), and the SIG 2-port muzzle brake on 1/2x28 threads.

The 16-inch cold-hammer-forged carbon steel barrel runs a 1:7 twist with black nitride finish and a free-float M-LOK handguard. The Regulator ships in FDE Cerakote with a two-stage match trigger from the factory, which is the trigger most other MCX configurations omit. Optional Romeo 2 red dot bundles are available for dealers that stock the optic-included SKU.

This is the high-end compliant choice for buyers who want piston operation, MCX modularity, and normal AR-15 magazine logistics in a non-pistol-grip stock layout. The trade-off vs a FightLite SCR or CMMG Dissent is price for the piston system and the SIG aftermarket footprint.