I suspect a fabrication, intended to look like a real Russian or (early) Prussian Helm. But the plate is certainly wrong for Prussia at any time (and sorry, Richie, the Gardes du Corps wore metal helmets, not leather). But the eagle should be crowned for either Russia or Prussia. Or for Austria's double eagle, for that matter. Also, if we look closely at the helmet, we see a relatively low crown. On the early helmets, from the 1850s and '60s, the crown was higher. In the case of Prussia, the crown was reduced in height by 1870, almost to the lower height it reached after the Franco-Prussian war. This one looks almost like a crown from a later helmet with the deeper visor and neck guard from an earlier helmet attached. The anchor is missing its bar, too, and the scroll has no text, no motto, etc. It may be genuine, from some small state or city-state, but I don't recognize it as from Russia or any of the German states.
Prost!
Brad