Mehul,

Interesting bit of info, I had no idea, I followed on this information and found the following:

"The concept of creating his own single shot rifle came about on an Alaskan hunting trip in 1973. He was accompanied by a gunsmithing school chum by the name of Gerhard Hartmann, founder, with Otto Weiss, of the respected firm of Hartmann & Weiss, Hamberg. Hartmann was shooting his company's version of the Heeren single shot rifle, an older design that a few different German and English gunmakers had used. Hagn told Hartmann, "I will make a better one.""

"During this refinement period both Hagn and Hartmann & Weiss built actions and rifles on this design. The left side of the breech block of the rifle I wrote about in 2001 carries Hartmann & Weiss markings."

From: http://www.martiniandhagngunmakers.com/technicalinfo.htm

-Trev