Sig Sauer MCX: Weapon that Omar Mateen was reported as using at Pulse event.

https://www.washingtonpost.com/news/checkpoint/wp/2016/06/14/the-gun-the-orlando-shooter-used-was-not-an-ar-15-that-doesnt-change-much/?utm_term=.92d08ac93f9f

Excerpt: Originally designed for U.S. Special Operations forces, the MCX was built from the “ground up” to be lightweight and short, and it accepts “a broad array of accessories, enabling you to build a complete weapon system for any scenario or environment,” Sig Sauer’s website says.