I'd say that possibly the same artisan performed the tap, tap, tap or more likely they differ by one be the master & the other his student. Engraver Hugo Kolb was Georg Lindner's Brother-in-Law & Fritz Heimbeck was a student of Kolb.

http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=236738

Kind Regards,

Raimey
rse