The M8C is a .50 caliber self-loading rifle designed to mount on top of the 106mm M40 recoilless rifle. The recoilless rifle creates a massive signature when fired, and so it is imperative that operators move immediately after firing. In order to make accurate first-round hits, the M8C was built with a unique 12.7x77mm cartridge which matches the trajectory of the 106mm round. Using a tracer-spotter projectile, the M40 gunner is able to adjust aim with spotter rounds that will not be noticed by the target and ensure a good hit with the first 106mm shot.
This example has been fitted to a tripod for shooting, which its not historically appropriate – but is convenient.