Before WW II Zbrojovka Brno make experiment with a number of types anti-tank rifles in a few calibers (15mm, 12mm and 7,92 mm). Along WW II were manufacture rifles for cartridge personal construction 15x104 (15 mm Besa). These cartridges have had indeed small effectivity.
Cartridges on photograph are Czech experiment 7,92 mm ZVV (7,92 x 145). Cartridge case be real two-piece - iron head and brass cartridge case. Head is able to have two longitude - 22 mm (photo) and 8,6 mm. Sort on weight powder meanwhile isn’t know. Bullet has been probably armour-piercing, weight now also isn’t know. From archives Zbrojovka Brno succeed find out data for speed - muzzle velocity is 1.270 - 1.320 m/s. This is very very high gear and penetration have to be very good. These cartridges wasn’t normal manufacture.
In the year 1941 Zbrojovka Brno construct experimental cartridge with calibre bullet 15 mm. Was be named “15 mm PzB 42”. Cartridge case had longitude 156 mm and originate adaptation case for 20 mm Solothurn. Muzzle velocity has been 1260 m/sith, weight armor-piercing tracer projectile 80 gramme. Cartridge was only experimental.