HK XM8.

The Heckler & Koch HK XM8 was an experimental modular assault rifle system that underwent trials with the US Army in an effort to become its next standard-issue assault weapon system. The firearm was to replace the long-running Colt M16 rifle and M4 carbine forms. As such, the XM8 was to become its own family of automatic weapons to include the basic assault rifle (that could also double as a designated marksman rifle), a shortened carbine (with support for the experimental XM320 grenade launcher), a dedicated sharpshooter's version and a compact carbine with optional collapsing stock. Despite the program's promising results, the XM8 was suspended in April of 2005 before seeing official cancellation in October of that year.