Hotchkiss used a ribbon type mainspring. The hammer was mounted inside the breech block. This screen grab shows the mechanism in the context of his patent drawing:
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Below is the device in isolation, shown cocked:
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And shown again with the spring expanded.
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Expanded spring.jpg [ 52.87 KiB | Viewed 2608 times ]
His patent argues that because the spring simultaneously pushes up and pulls down, it produces less or perhaps more symmetrical wear on the mechanism. Another possibiity might be that he was "improving" his way around some rival patent. In any event, the ribbon spring is typical of the Hotchkiss series of QF's. Here is a photo taken long ago of a dismounted spring.
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Here is another view in a photo shot from underneath the breech block.
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Immediately to the right of the mainspring is a ratchet and pawl that operates on the cocking shaft and securely cocks the mainspring.
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Here is a view from below showing the centered hammer and mainspring and, offset to the right, the sear. A linear spring bears upward on the sear. The left end of the spring is solidly anchored in the wall of the breech block.
In this view the cocking shaft is rotated counter-clockwise until the pawl on the spring-loaded sear catches the ratchet. The mechanism is shown cocked.
Finally, shown below is an X-ray view of the hammer and sear mechanism positioned inside the breech block. At this point they are simply embedded in the block. Next step will be to machine away a cavity and mounts for this mechanism.
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Benjamin Hotchkiss's obituary noted that he owned the Empire Spring company in Saratoga, New York. Thinking this might be a spring manufacturing company -- that he had perhaps bought in one of his suppliers -- I googled it. It turns out the Empire Spring Company was in fact a hugely successful producer of spring water, like Evian or San Pellegrino. Full of surprises, his story.