Steve Laug published in his blog at rebornpipes a very deep and detailed investigation regarding Shamrock pipes. “There were two Shamrock lines—the Rogers Import U.S.-only line with the nickel band, and the Peterson unmounted line with a white “S” stamped on the mouthpiece. This line … debuted in the 1945 catalog in the 30 classic shapes then being offered, in both smooth and sandblast, always with a fishtail mouthpiece, and continued with the same finish and “S” stamp until the 1975 catalog”. We can only add that Irish B.P.L produced a series named “Golden Shamrock”.
So there’s a nice and well maintained Peterson pipe from 1945-75.
The pipe markings are “SHAMROCK \ “A PETERSON PRODUCT \ MADE IN THE REP. \ OF IRELAND”, “268”. The length is 15.0 cm (5.9″), and the bowl’s height is 4.5 cm (1.77″). External diameter of the bowl is 3.1 cm (1.22″), internal diameter is 1.9 cm (0.75″). The depth is 3.8 cm (1.5″) and this pipe weighs 31 gr. Briar, vulcanite stem, no filter. Here we had to replace a not properly adjusted replacement tennon, now the stem sits reliable and the repair is almost invisible. The pipe was moderately smoked and generally well preserverd. It’s completed with the pipe box (marked with another model, it’s a frequent situation when a seller in a tobacco shop takes the first available box to pack the pipe) and a Peterson’s “user guide”.