Does anyone have any information on a J BRECHTBUHL THUN martini? I've done a Google search and all I have found is a couple of pictures of one that sold on an auction. I recently  acquired a complete action. Any info would be appreciated.

Thun is in Switzerland so it is a Swiss Martini.

RR,
Can you post a few photos of your martini? I have a Swiss Martini in 7.5x55 GP11 that is marked K. Zimmermann from Luzern. From what I've read from limited resources it seems like most of the gunsmiths would purchase the parts and assemble the rifles. My Martini has a Hammerli marked barrel. I am guessing your maker similarly purchased the parts and stamped his name on the receiver per the norm. I find there seems to be less variation between Swiss Martinis from then same time period compared to the Germans. The Germans made several variety of Martini like actions whereas the Swiss kept to the design by old Frederich Martini.

The Swiss Martinis almost always are in the military caliber of the time. That is before 1890 they would be in the 10.4mm Vetterli cartridge. After 1890 to 1911 or so they would be in their Schmidt-Rubin 7.5x53 GP90 cartridge. And models after 1911 would be in their Spitzer GP11 cartridge. Before around 1930 their rifles would just have open iron sights and a fixed Swiss butt plate. After around 1930 the Swiss free rifle shooting rules allowed for diopter sights and slings. 

I'll keep digging more on your particular maker but that a start in the Swiss martini history.
Thanks,
-David

I have a Swiss martini chambered for 9.3x53 rimless, a rimmed version of the cartridge was available so the only reason I can think of for using a rimless cartridge is ammunition availability. The extractor works well.
Mike