I saw a number of engraving variations, but none which had the pattern on your gun. I agree with Drew: it appears to be a variation of the pattern on a pre-1913 No. 3 gun. The major variations I saw included (1) 5 shooters on each sideplate and (2) 5 shooters on one sideplate with a single shooter on the other. Sometimes the 5 shooters were in a straight line, sometimes they were in a staggered line. With a magnifying glass other small differences in the patterns could be detected, I believe simply due to the fact that the engraving was all hand work.
I find your gun really interesting. You might consider writing an article for the Journal, with pictures. I'm sure the editors and the membership would appreciate it, and it could be a valuable reference next time somebody writes an article about Trap Grades.
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