Indeed Robert Schrader Jagdwaffen did in fact use leaf springs in patent 180584 from 1906 and an image is found here:

http://www.shotgunworld.com/bbs/viewtopic.php?f=2&t=217327

I'll have to do some digging but if I am not mistaken his previous designs were centered around coil springs and the patents will tell the tale. DRP 137824 for the Schildzapfenverschluss of his may have been we he made the transition from coil to leaf. I think it was loosely based on U.S. of A. Patent 394,691 of 1888 by Elmore Adelbert Harris's hingpin design: http://www.google.com/patents?id=Z_5CAAA...p;q&f=false or some similar patent by Elmore Adelbert Harris.

Kind Regards,

Raimey
rse