So long as I know there is a drawing in several books about a German
explosive round with conical point from WWI. ( see also Kent`s book page 24 )
First picture is a French report from 1922 that mention the bullet with no further details.
On the second picture you see the technical information on each bullet they examine
except the bullet in question,all the lines are empty.
Years ago I bought a round that looks like the round mention in many books.
Recently I could use a X-Ray machine and following picture reveal.
Headstamp H / 5 / 18 / S67 / bullet with plain unclad jacket.