All Merkels are fixed chokes as far as I know. Actually I would not want to own a hand built double with interchangeable choke tubes. They are "vastly overrated" for use in hunting guns in my opinion. Choke tubes require that the barrels be too thick for proper balance and handling, and the only way around that is to flare the ends of the barrels to accommodate the threads. Someone will chime in that "thinwall" tubes solve both problems, but they still are limited in their construction and patterning ability. Merkels are individually hand patterned at the factory. They must hit point of aim and with the proper pattern density for the choke designation before they leave the factory. The fixed chokes are longer than typical removable tubes, and have a parallel section to aid pattern uniformity after the shot is squeezed through the tapered section. They DO pattern better. The older ones are set up for fiber wads, and typically shoot a bit tight for choke designation with plastic shotcup wads. A very skilled shotgun smith can open up any old, tightly choked gun to a more moderate choke and taper the forcing cones for plastic wads. There are only a few smiths in Canada skilled enough to do that properly on a Merkel or similar hand built double.
My gun is very used, from the 1950's or thereabouts, but not the least bit "worn out" - I don't think it is possible to wear out a Merkel by hunting with it. It is a two barrel set with 16/16 2-3/4" ( 70mm) Improved Modified over Modified ( 3/4 over 1/2 choke) and 16/70mm 1/1 choke over 7x57R with a claw mounted 4x scope. It was a private sale, but I did see some like it on Martini Gunmakers site.
