Up for sale is a factory custom SIG Sauer M400 SDI upper receiver, lightly used and in excellent condition. This is not your standard M400—this upper comes factory-marked and built with premium upgrades that are getting harder to find.
It features a 14.5” barrel with a pinned flash hider bringing it to a legal 16” overall length, chambered in 5.56x45mm, making it a perfect balance of maneuverability and performance.
What really sets this apart:
This upper is a turnkey setup with premium components already installed—no need to spend time or money upgrading. Between the discontinued rail and high-end accessories, this is a rare, well-rounded build that stands out from standard offerings.
Perfect for anyone looking for a reliable, upgraded, and harder-to-find SIG setup.
