M242 Bushmaster 3D model

The M242 Bushmaster is a 25 mm (25×137mm) single-barrel chain-driven autocannon. It is used extensively by the U.S. military, as well as by NATO's and some other nations' forces in ground combat vehicles, such as the Bradley fighting vehicle and various watercraft. Designed and manufactured originally by Hughes Helicopters in Culver City, California.[1][2] The company was acquired by McDonnell Douglas Helicopters in 1985, which merged into Boeing Corporation in 1997.

From wikipedia.

High poly closest design.