The Winchester 1903 was produced between 1902 (available in early 1903) and 1932, although sales continued at least until 1936, and was designed by Thomas C. Johnson (additionally the designer of the Model 1905, 1907, and 1910 rifles, and the 1911 shotgun). Something over 126,000 were produced in total, all chambered for the .22 Winchester Automatic Rim Fire (not the same as the .22 Winchester Rim Fire for the Model 1890). There was also a similar .22 Remington Automatic, but the two are not interchangeable.
Serial number 181xx would be from about 1906, and should be marked "MOD. 1903" on the barrel, just forward of the receiver. In an attempt to make their models seem more modern, Winchester began eliminating the "18" and "19" from the markings on all models, and around 1912 the model designation was changed to "MOD. 03". The "MODEL 03" marking was first used around 1928.
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