Hello , maybe I can help you . It is not gestoinbohr , but gesteinbohr . Stein means rock Bohr means the material to make a hole .
So 'gesteinbohrkp.8' means the 8° company dealing with heavy material such as breakhammers etc . See also the following German URL Abrbreviations in the German army
http://ostbataillon.fromru.com/ek-g.htm
Greetings from Belgium
Patrick Praats