Hands down, this is one of the coolest things you will see all day.
“The Lahti L-39 is a Finnish 20mm anti-tank rifle used during the second world war. It had excellent accuracy, penetration and range, but its size made transportation difficult. The rifle is a semi-automatic, gas operated weapon with the piston located beneath the barrel and ammunition feed from detachable top-mounted magazine with bottom ejection for the spent cartridges. To reduce recoil, the rifle is equipped with a five hole muzzle brake and a padded leather recoil pad.”