IMHO, the "LK" is the barrel maker's mark - most likely Louis Kelber, who AFAIK was active near Suhl.
That mark was used by the Gebrüder Kelber barrelmaking company, founded by Louis Kelber in 1894, owned then by Louis, Robert and Wilhelm Kelber (WK).
They usually used either an L stamp or an LK.
In 1927 the "Gebr. Kelber" company was dissolved, but both Louis and Wilhelm Kelber started again on their own, Louis using the "LK" stamp and Wilhelm the well-known "WK".
Your Drilling appears to have been made the year before they started separate companies.
Last edited by PetahW; March 14, 2013 at 02:48 PM.