1867, 09 Feb - Stanton patent 367 - rebounding hammers
1869, 30 Dec - Stanton patent 3774 - rebounding hammer modification

It took awhile for the invention to take hold but it was so logical and good, a lot of older guns were subsequently modified. Given that pin-fires dominated the market up to 1870-72, it's entirely possibly that there were pin-fires with rebounding hammers.

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