“...I have seen ONE photo of a Union soldier holding a Spencer with the coffee grinder handle in the stock. ...”
Call the archivists and documentarians then. Assuredly a rare variant.
Given that ingenuity of American troops, I’d never reject out of hand the possibility that some enterprising private shoehorned a coffee mill into the stock of a Spencer.
And the 1860s - early Industrial-Age America - were a time of unprecedented experimentation and innovation, in firearms and much else.
James Wolfe Ripley - Chief of Ordnance for the Union War Dept as the American Civil War began - is condemned today for lack of interest in breechloaders and repeaters, but his overriding duty was to organize the production of standard issue arms. He regarded the horde of inventors that stormed Ordnance offices, each toting their personal “great idea” to save the Union by armed force, as a gaggle of starry-eyed fools wilfully devoid of meaningful experience.
And it is very true that in 1861 no metallic-cartridge small-arm system was in any way a battle-proven concept. The Federal government wanted proof before betting military monies.
Actually I have the photo, it also contains my Great Grandfather in his confederate uniform. The rifle is most assuredly a Spencer and does have the handle in it. Obviously captured from some prisoner or dead Yankee soldier.
Because of this photo I always thought the coffee grinder must have been fairly common.