Hello Robert,
this is exactly what I meant.
Maybe others don't noticed the well worked and exact solvering of the brass part, exactly like I've seen it by old/antique examples, the same with the well chosen copper end plate, again like I've seen it before originally. At last the perfect patina match of the brass with the original fittings, very good.
Regarding brass and copper bladed daggers/knives I also only know the possible reasons you have numerated already. But what I have seen until now is that all this daggers and knives would do the same job as a steel bladed counterpart IMVHO. So maybe you can find them just because iron wasn't at hand.
But your incoming example could be indeed a powderman's knife. Courious to see your pictures.
Regards,
Detlef