Rifleman Q&A: Roos Underhammer Muzzleloader

posted on November 28, 2021
gun muzzleloader upsidedown mechanism yellow table screens threads steel wood

Q. I have an unusual muzzleloading, small-bore, under-hammer rifle in my collection. The top of the barrel near the action is stamped “U. Roos & Sohn in Stuttgart.” The ignition system uses a percussion cap, which is placed at the bottom of a hole bored in the action. A firing pin is then placed in the hole, which is followed by a large wing nut that is threaded into the hole. The wing nut has a hole in the center for the firing pin. I would really appreciate any information you can give me on it.

A. It indeed looks like you have a pretty interesting underhammer. One of the continual problems with any underhammer design was the priming aspect—any cap that was loose would fall off the inverted cone. The wing nut retainer solution that Roos came up with seems to work, but would have been slow for the second shot. Screwed slightly on, the unit might have also served as a safety feature.

Roos & Sohn was one of the better known gunsmithing establishments in Stuttgart, Germany, from 1845 onwards. The National Firearms Museum has in its collection a .410 shotgun made up by this firm for the foreign market. Unfortunately, Allied bombing raids in 1945 destroyed all records for this company.

This “Questions & Answers” was featured in the January 2005 issue of American Rifleman. At time of publication, "Questions & Answers" was compiled by Staff, Ballistics Editor William C. Davis, Jr., and Contributing Editors: David Andrews, Hugh C. Birnbaum, Bruce N. Canfield, O. Reid Coffield, Charles Q. Cutshaw, Charles M. Fagg, Angus Laidlaw, Evan P. Marshall, Charles E. Petty, Robert B. Pomeranz, O.D., Jon R. Sundra, Jim Supica, A.W.F. Taylerson, John M. Taylor and John Treakle.

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