The 6.5×58mm Vergueiro is a centerfire rimless cartridge designed in 1904 specifically for the Mauser-Vergueiro, chosen as service rifle of the Portuguese Army.

Smokeless powder allowed for a higher velocity round and further calibre reduction to 6.5 mm, a step already taken by other European countries, e.g. Sweden (6.5×55mm Swedish) and Italy (6.5×52mm Carcano).

It remained the service rifle cartridge until the Karabiner 98k replaced the Mauser-Vergueiro pattern in 1939.

In military use the common projectile weighs 155 grains and travels at up to 2,400 feet (730 meters) per second.

A lot of the Mauser-Vergueiro rifles were later rechambered to accept the standard 7.92×57mm cartridge of the newer Mauser 98k pattern.