In addition to barrels, they were busy with 20mm x 113mm Aircraft Machine Gun cartridges. The Finnish also used a 20mm x 138mm semi-auto rifle cartridge. It is basicly a scaled-up belted .300 H&H Magnum cartridge. DDR
Excellent find, very impressive - this is very rare ammunition to find nowadays. IMHO labeling it as aircraft ammunition is bit misleading.
Lahti did some work with 20-mm aircraft cannon in this caliber, but didn't get beyond prototype or two - as far as known none of which saw combat use. The non-belted version 20 x 113 was used mainly in Lahti L-34 automatic cannons - for which there were two or three prototypes and small production series of 12 guns. Those dozen guns (known as "L-34 version II") were issued to Finnish Navy, who used them to arm some motor patrol boats (so called "VMV-boats"), but their service life with Finnish Navy proved short since the Navy apparently replaced them with much more plentiful 20-mm Madsen guns after Winter War. Another weapons using this ammunition were two Lahti L-39 antitank-rifle prototypes, which were issued and saw some combat use during Winter War (once the mass-production of L-39 started after Winter War, the mass-production version was chambered to 20 x 138B ammunition because that was already used in German-made 20-mm AA-guns acquired by Finnish Army and supposedly because the 113-mm long cartridge case run out of volume for adding propellant). All these guns were manufactured by VKT (Valtion Kivääritehdas = State Rifle Factory) in city of Jyväskylä.
The even more rare Finnish ammunition type is belted version 20 x 113B - it was used pretty much only in two L-34 automatic cannon prototypes manufactured by Tampella factory in city of Tampere. The two guns were used as air-defence weapons of Tampella factory during WW2. They used quite a bit of ammunition shooting towards Soviet aircraft, but as far as known failed shooting down any. Their gun-crews were Civil Guard members belonging to factory workers.
Muzzle velocity for 20 x 113 and 20 x 113B ammunition was around 830 m/sec. Armour penetration from 300 meters in 60 degree angle was around 17 - 22 mm.
For obvious reasons (20 x 138B Solothurn Long becoming standard ammunition type for Finnish 20-mm antitank-rifles and most of anti-aircraft guns) Tikkakoski started manufacturing also this ammunition during WW2.