Lilja Model 1943. Prototype of the Finnish assault rifle. Inspector Erkki Lilja, a close colleague of Aimo Lahti, was interested in the use of intermediate cartridges around that time. Thus, Lilja developed the design of his assault rifle also in 1943. At the end of that year, he manufactured a prototype at VKT facilities without official approval from the company, but left the weapon unfinished
It remained that way until the 1970s, when Lilja finally finished building the rifle and retired. Very little is known about the design of the rifle, and speculation comes from the very few available photographs. The weapon uses a 30-round detachable box magazine and (most likely, but not certain) a blowback action. The Sturmgewehr uses Lilja’s proprietary 9×40mm cartridge, essentially a longer version of the .30 Carbine round
9x40 Lilja / 9 mm Finnish Lilja XPL Model 43 / 9x40 Finnish experimental 1943 / 9x40 Finnish XPL Lilja M-43 / 9x40 Lilja
The cartridge was developed on a private initiative in 1943 by Finnish gunsmith Erkki Lilja, an employee of the state arms factory Valtion Kivääritehdas (VKT), a colleague and comrade of Aimo Lahti. The ammunition was intended for an experimental prototype of his own assault rifle and was built, according to some sources, on the basis of an extended casing of the 9 mm Parabellum pistol. Other sources indicate a similarity of the design idea with the American .30 M1 Carbine, but in an increased caliber. The direct production of a batch of cartridges was carried out in the same year by the Finnish state cartridge factory from Lapua Valtion Patruuniatehdas (VPT).
According to available information, the Finnish military leadership of that time did not have the opportunity to introduce an intermediate cartridge, focusing on maintaining the operability of the existing small arms systems. The signing of the Moscow Armistice (1944) between Finland, the USSR and Great Britain made further research in this direction irrelevant and led to the curtailment of the relevant projects, including the one under consideration. This circumstance is considered one of the key ones, leaving this cartridge and weapon within the experimental framework.