Unknown clone of M1842. I tried to find it in ABC, the closest match is ABC N 1846. Mine example has no markings, though is should had been manufactured in Germany (or Belgium?).
Distinctive features are : fuller shape, spring fixed with a screw, one rivet on the opposite side on 7th rib, ring diameter 23,2mm.
For my eye the only difference is that the rivet is polished to the level of surrounding brass.
I’ve made some pictures to show the difference of the fuller shape vs Chassepot and ring diameter, fuller shape and hilt length vs Mutzig 1842.
Another similar one, but slightly shorter, is ABC N 1748.
Anyone having clear identification please let me know.