You may be right Guy. I forgot that this model was reported to have all frames stamped and manufactured before 1899, making all antiques. The question of when it was shipped needs a letter to be sure, but the low serial number frames would have been manufactured early in production as I guessed 1878 was the manufacturing date of the frame and not the ship date.

Perhaps the OP can measure the length of the cylinder? It looks like it might be a 1 7/16" to me?

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Gary
SWCA 2515