If you are sure of the "RZ", the tubes would have been made and assembled by R. Zimmermann of Suhl. It may have been made by or for Carl Zimmerman of Zella-Mehlis, whose craftsmen were considered by the Suhl craftsmen to be a rung below. Carl Zimmerman began in 1857 and peddled everything hunting. This could be one of his last examples as I don't think his firm survived the aftermath of the effects of WWI. More than likely finished by a Zimmermann and there may other marks to build a solid case. The "705" is probably the 705th to pass thru the proofhouse that year. Any other interesting marks to note the specific proofhouse? The shape of the receiver, the Greener safety, the position of what looks to be the cocking indicators both in combo with the underlever hints at a Treff action with the coil spring strikers in a metal block attached to the top tang. Usually there's an odd screw thru the top tang that along with the position of the cocking indicators which gives it away as being a Treff action but I don't know that I remember one being fitted to an O/U.
Kind Regards,
Raimey
rse
