Pre WW1 prototype anti-tank rifle?

[World B4]

The Mauser-Ladera M1913 was a prewar german project to develop a semiautomatic rifle to fire armor piercing 7.92x57mm rounds to damage fortifications. Had the rifle gone into service, it would almost certainly been used against belgian armored cars, and later in the war, british tanks, like the easily penetrated Mark 1 and 2. Information is scarce, and I'm a bit worried that it is a hoax. Can anyone here provide more information about the project?

 

[drejr]

The only source I know of is the Russian book "Faustnik in Action." From the picture it looks like a Mauser Selbstlader with a pistol grip and very long barrel. Probably intended for use in fortifications - there's a ring that may be for a pintle mount.

I suspect "Ladera" is a corruption of "lader."

 

[World B4]

https://twitter.com/jmantime/status/927486641954021376

idk how credible this is but here

thoughts?