The rifle is a semi-automatic, gas operated weapon with the piston located beneath the barrel and ammunition feed from a detachable top-mounted magazine with bottom ejection for the spent cartridges.

The gun was also widely[clarification needed] used in the "cold Charlie" counter-sniper technique, where the Finns would use mannequins posing as sloppily-covered officers.

Although the weapon was not able to penetrate newer Soviet tanks like the T-34 and KV-1, it still proved to be quite effective against bunker loopholes and embrasures, long range targets, and even aircraft.

Other good targets were snipers, and several weak spots on tanks, such as open top hatches, especially with phosphorus ammunition.

[2] Several of the rifles remained in service after World War II serving as anti-helicopter weapons, while many others were sold to collectors, mostly in the United States.

Because the weapon fires rounds larger than .50 caliber, it is considered a destructive device and is subject to the 1934 National Firearms Act.

Instead, a rotating crank lever on the right side of the gun, operating a rack and pinion, is used to pull the bolt back.

By the end of the war over 1,900 L39s had been manufactured by VKT (Valtion Kivääritehdas, "State Rifle Factory", modern day Patria) and put in the field.