Description
SIG Sauer MPX K SBR, 9mm, 4.5-Inch Barrel, Black, 35-Round
The SIG MPX SBR is SIG’s 9mm piston firearm. The MPX runs a short-stroke piston and AR-style controls on 9mm, with magazines that are SIG’s own MPX pattern.
It does not take Glock, P320, or AR-15 magazines. The top rail is optic-ready. A factory optic is not installed. Pistols ship with SIG’s folding PCB. The SBR uses a stock and needs NFA paperwork.
This configuration
Copperhead and the MPX K pistol go to a regular FFL. The 16 in. PCC is already a rifle, so you do not need a tax stamp for barrel length. This 4.5 in. gun with a stock does. It ships to a licensed Class III / SOT dealer. You need the NFA transfer and approval before you take possession. Confirm federal, state, and local rules before you order.
What ships
A factory optic is installed only when this page says so. This item ships to a licensed FFL. See the SIG MPX collection.
Specifications and Included Items
- Model: RMPX-4B-9-35-SBR
- Platform: MPX K SBR
- Caliber: 9mm Luger
- Barrel: 4.5 in.
- Operating system: Short-stroke piston, closed rotating bolt
- Stock: Folding stock
- Finish: Black
- Magazines included: One 35-round MPX magazine
- Sights: Optic-ready rail; no factory optic
- NFA: Short-barreled rifle; Class III / SOT transfer required







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