Gents,
look at your Larcade Volume I, pages 87-88.
This helmet was worn between 1867 and 1870 in the Oldenburg IR 91.
This Wappen was the first Oldenburg Wappen pattern (1843-1870) till the AKO of the third of March 1870 gave the OJR91 a new plate, the Linien-Adler with small Oldenburg Wappen in the middle.
Starting 1843 till 1867, this particular Wappen was worn on a very particular (ugly)helmet which had a very specific spike, directly fixed on the skull, without spike base.
Starting the 15th of July 1867 till 1918, the OJR 91 adopted the prussian spike helmet style.
Philippe :salute: