A bit of detective work. I obtained a very nice M-15 pickelhaube, liner in first class condition, but missing spike/ball. So who used it, infantry or artillery? Markings were not overly helpfull. Hand painted in white on the neckguard: 7. III on one side, 3 on the other. It was brought back after the war by a member of the 71st Artillery Regiment, U.S. Coast Artillery Corps, AEF, deployed to France from August 1918 to February 1919. It seemed to me that an artilleryman would be more likely to bring back an artillery helmet, and the 7. seemed the most likely regimental number, but one couldn't be sure.
I checked and found that 3 IR used the Grenadier Wappen, while 7 IR used the Grenadier Wappen with bandeau, which seems to rule out the helmet as one from the foot regiments. The 3 FsAR used the 1st pattern Grenadier Wappen, as did 3 FAR, while 7 FAR used the Grenadier Wappen. That left 7 FsAR, which used the standard line Prussian Wappen. The Roman numerals would seem to be the bataillon number, which leaves the battery. In that case, I would think its almost certain that this helmet was used by the Westfalisches Fussartillerie-Regiment Nr. 7, III Bataillon, 3. Batterie. Does anybody have any thoughts on this?