I suppose a valid attempt to date these old top-breaks would be to take the number of years and the total built to come up with an average made per year. Not that accurate, but it would cost your government money and time to refute the data, so may be good enough.

Only truly valid option would be to spend $50 and get a letter from the factory, but that takes quite a bit of time and would not be cost effective to date a gun you may not be able to buy.

Good luck on your quest.

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Gary
SWCA 2515