The Mathieu action was built by the Mathieu Arms Company of Oakland, CA. It was a custom-built very expensive action. Introduced around 1950 and disappeared around 1960. The action body and bolt were machined from single pieces of steel. Has features derived from the Winchester 70, the '03 Springfield, and the 1917 Enfield. Frank de Haas has a favorable write-up on them in his Bolt Action Rifles, copyright 1971. Frank de Haas says they were most commonly used for building Weatherby calibers in the 1950s. de Haas further says that there is little mention of the Mathieu action in any magazines or other literature and most knowledge about them was favorable word of mouth. de Haas examined one for his book that had survived multiple barrels in Weatherby calibers and showed no wear.
The action in the picture has never been barreled or stocked. Have had it for at least twenty years and have never gotten around to building anything on it. (Have a bad habit of accumulating anything left-hand.) Thinking of someday building a fifty caliber something on it.