The SIG Sauer MPX (SIG Sauer part no. WRMPX-4B-9-SBR-35) is a short-barrel-rifle configuration of SIG’s proven MPX submachine-gun-pattern platform, chambered in 9mm and built on SIG’s fully ambidextrous, gas-piston-operated MPX system. This specific configuration is a First Responder Firearm, sold exclusively to eligible law enforcement, military, and qualifying first-responder buyers rather than the general public.

Key Specifications

• Chambered in 9mm, matched to SIG’s gas-piston-operated MPX action.
• Configured as a factory short-barrel rifle (SBR) under the MPX platform.
• Restricted to first responder and qualifying professional buyers only.
• Ships with a 35-round polymer magazine.
• Fitted with a collapsible stock for a compact overall length.

Frequently Asked Questions

Who can buy this firearm? This is a First Responder Firearm, sold exclusively to eligible law enforcement, military, and qualifying first-responder buyers — it is not available to the general public.

Is this an NFA item? Yes. As a short-barrel rifle, it’s a Title II firearm requiring an approved ATF Form 4 and transfer through an NFA-licensed dealer, in addition to confirming professional eligibility.

What caliber does it use? 9mm, matched to SIG’s MPX platform.

Buy the SIG Sauer MPX SBR

This is a Title II item regulated under the National Firearms Act. Purchase requires an approved ATF Form 4, no federal transfer tax and transfer through a licensed NFA (SOT/Class 3) dealer, with an extended federal approval wait before delivery. This model is also restricted to verified first-responder and professional buyers. Contact our Lubbock, Texas team to confirm your eligibility and walk through the NFA transfer process for this SIG Sauer short barrel rifle.