I suspect that the gun was dropped and landed on its hammer, leaving a broken tip. Rather than replacing the hammer, the owner just cleaned up the break as well as he could with a file and kept on shooting.

With the patent stamp on it, that's a company hammer.

I have a prewar Kit Gun (same action) with an enlarged hammer spur. I figured it was a repair after the original hammer was broken. Not sure why a shooter would willingly grind down the hammer on a target revolver. Most of the mods made the hammers bigger.

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David Wilson