What a folly that would have been. What . . . and have the soldiers waste ammunition? Pretty much why the Europeans were able to dump all of their obsolete rifles to both the north and the south - their weaponry was advancing - with obsolete generals like Winfield Scott in charge, why would you want to supply the troops with something that they'd burn up ammo in? Let's face it, it was mid war before the advantages of the Spencer and Henry became evident.
Yes, the machinery might have existed that could make it, but the mind set wasn't there. BP was still in wide use everywhere with it's own unique problems of fouling, etc. As has often been said . . . "Everything in its own time".
If a pair of '51 Navies were good enough for Billy Hickok, then a single Navy on my right hip is good enough for me . . . besides . . . I'm probably only half as good as he was anyways. Hiram's Rangers Badge #63