SIG Sauer M400 PRO 5.56 16-inch Rifle

The SIG Sauer M400 PRO is a 5.56 NATO AR-15 (SIG Sauer part no. WRM400-556N-16B-PRO) built as SIG’s take on what an AR-15 should be, with the upgrades most shooters end up adding themselves already installed at the factory. It ships with a free-floating M-LOK handguard for better accuracy and handling, along with a quality grip and a premium 6-position buttstock featuring integral QD sling points. Ambidextrous controls come standard, so the M400 PRO runs equally well from either shoulder, and the Enhanced SIG Trigger helps shooters extract every bit of accuracy from the rifle’s lightweight 16-inch nitride barrel. A SIG Micro-Light Gas Block keeps the front end trim without sacrificing reliability. It’s a well-rounded carbine for range use, home defense, or as a dependable first AR-15 built with SIG’s reputation for quality.

Key Specifications

• Chambered in 5.56 NATO for reliable, widely available performance.
• Fitted with a 16-inch nitride-treated barrel for durability and accuracy.
• Uses a SIG Micro-Light Gas Block to keep the front end trim.
• Wears a free-floating M-LOK handguard that improves accuracy and handling.
• Includes a premium 6-position buttstock with integral QD sling points.
• Equipped with the Enhanced SIG Trigger for a crisper, more consistent break.
• Runs standard ambidextrous controls for confident use from either shoulder.

Frequently Asked Questions

What caliber does the M400 PRO shoot? It’s chambered in 5.56 NATO, the standard AR-platform cartridge.

Are the controls ambidextrous? Yes, the M400 PRO ships with standard ambidextrous controls for use from either shoulder.

Buy the SIG Sauer M400 PRO

Shooters who want factory upgrades already installed should take a close look at the M400 PRO. Order this SIG Sauer rifle from our AR rifle selection at Schaefer Defense, and we’ll ship it insured to your local FFL from our Lubbock, Texas shop.