Worlds most powerful heavy machine gun?

Answer 1

A likely candidate for 1st place would be the Russian Vladomir KPV Heavy Machine Gun, in caliber 14.5 x 115. These are capable of penetrating 32 mm of steel armor at 500 meters.

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Concur with above, though a couple things should be noted. The Chinese have a relatively new machine gun design called the QOJ-02, which fires the 14.5x115 cartridge as the KPV.

Also, it should be noted that a more powerful machine gun was developed in Belgium. It was known as the BRG-15, and fired a 15.5x115 cartridge which outperformed the Soviet 14.5x115. Although the end of the Cold War ended that programme, a limited number were produced, and mass production still remains a possibility.