In the 1930s, Poland decided to develop an anti-tank rifle, and the young designer Józef Maroszek came up with the winning system be scaling up a bolt action service rifle he had already drawn up. The project was kept very secret, out of concern that Germany or Russia would up-armor their tanks if the Polish rifle's existence and capabilities became known. This secrecy has led to a lot of misconceptions about the rifle today...

Interestingly, the ammunition for the wz.35 used a plain lead core. Polish engineers found that at its incredible 4200 fps (1280 m/s) muzzle velocity, the lead core had excellent armor penetrating capacity. When the German Army later captured and reused the rifles, they didn't trust this, and reloading captured Polish ammunition with German tungsten-cored projectiles made for the PzB-39.

Rather than explain the full story of the wz.35 in detail here, I will refer you to http://www.forgottenweapons.com/wz-35/ , where I have posted a full monograph on the rifle written by Leszek Erenfeicht.

Many thanks to the Royal Armouries for allowing me to film and disassemble this rifle! The NFC collection there - perhaps the best military small arms collection in Western Europe - is available by appointment to researchers:
https://royalarmouries.org/research/national-firearms-centre/

You can browse the various Armouries collections online here:
https://royalarmouries.org/collection/