Heavy machine gun
Heavy machine gun is a term used to describe automatic firearms which are too heavy for one soldier to carry.  In the early 20th century most were 7.62mm or .30 caliber. Nowadays the rounds fired by a heavy machine gun are .50 cal, which is 12.7mm x 99mm, or bigger. The largest in commonplace use are Russian designs which fire rounds of 14.5mm caliber. Bigger ones are called autocannons.