The First M4 to Earn the SIG Name.

We didn't set out to make just any M4. Instead, we used the innovation, performance and attention to detail that defines other SIG rifles to evolve the platform. The result is the SIGM400, a superior system offering advanced features available right out of the box that were once only found on the after-market.

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Direct Impingement Gas System

The M400 features a direct impingement gas operating system, common to the traditional AR platform, with a rotating locking bolt.

After-Market Upgrades Made Standard

An extended charging handle latch allows for fast and easy access with optics mounted on the flat-top upper receiver. A built-in tensioning device eliminates accuracy-robbing play between upper and lower receivers. Ambidextrous controls make the SIGM400 series a perfect fit for right- or left-hand shooters.

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