Most interesting that Louis Kelber & the mechanic EW both contributed effort on the tube work along w/ the owner of the boxed Ks or K in a Rhombus. For that effort, one couldn't ask for anything better. Not sure on the DRGM(Gebrauchsmuster) 1116 but I seem to recall that DRGMs commenced on June 1st, 1891 and considering the voluntary proof data, this example should have been completed by 1893?

http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=389535

Thread on Heym's patent.

Cheers,

Raimey
rse