Have you noticed that the word "Monopol" is also incorporated into the Witten steel trademark? "Monopol" was then also a "Trademark" for a better-quality barrel steel by that company. There are no other markings that hint to Belgium. Trademarks were not internationally protected as they are now. Often lesser makers used marks that intentionally resembled those of "name" competitors. Note also the "3 rings", resembling the Krupp trademark! There is no need to speculate about a Liege/Francotte connection! "Monopol", as well as "Ideal", "Triumph" and other such euphemistic expressions, were used by many makers and dealers for many different products then. FI I remember cigars named "Monopol", and I know about half a dozen entirely different gun actions called "Ideal" by their hopeful inventors or dealers. IMHO the illegible letter under the anchor stands for the maker, while the Z stands for Zella. The neighbouring towns Zella and Mehlis were only amalgamated to Z-M in the 1920s.
The Gusstahlfabrik (cast steel factory) Carl Berger&Co, later Gusstahlwerk Witten AG, then led by Carl's son Louis Constans Berger, in the 1860s pioneered the use of barrel steel. Besides providing the steel for the Dreyse needlerifles of the Franco-German war of 1870-71, they exported lots of barrel steel to the USA in the early 1870s. Among these exports were large amounts of special-order, large diameter round stock. Their main American customer was Colt in Hartford. So your "all American" Colt Peacemaker most likely has a barrel and cylinder made of Witten steel!
This Drilling was almost certainly made in Zella-Mehlis, evidenced by the finer underlever details, before 1911. In 1911 the Z-M proofhouse made the change from the old-fashioned gauge numbers to tenths of millimeters. So we can narrow down the dating from April 1, 1893, when the 1891 prooflaw came to force, and 1911. According to the German 1891 proof tables the gauge number 67,49 stands for a plug gauge of 10.41mm = .410" diameter that would pass the barrel. The next larger number, 62,78 = 10.67mm = .420" did not pass the barrel at the proofhouse then. These numbers, as the later mm numbers, stand for the bore or land diameter, not for the groove/bullet one! You have to add the depth of the grooves to get to the bullet diameter. Without a chamber cast determining the chambering is impossible. The 11.15x65R aka 11mm Drillingspatrone was only one of the series of LK cartridges, all based on the brass 36 gauge/.410 case. These once came in lengths of 40, 50, 52, 55 and 60 mm besides the already mentioned 65mm. But in the 1890s there were as many varieties as in Heinz Mixed Pickles, as apparently every country gunsmith on opening his own shop first designed his own proprietary rifle cartridge.
