Since I just posted this on Jan Stills forum, thought I would just cut and paste it here:
Hello fellow collectors. I believe I may have solved the mystery of the "Kü" marking. Background, some may know me some may not. I am active in the K98k collecting field and have co-authored a few books on the subject. We are working on Volume 2 in which I will cover the repair depots that repaired K98k's. In doing so I have acquired a bit of a feel for how the Germans marked depot weapons and such. For the Heer, the typical abbreviation for depots uses the first and last letter of the depot: for instance Spandau is shortened to Su, Mainz is Mz, Krakau is Kru, and these abbreviations were applied to the rifles in the way of inspection stamps to show the repair facility responsible to doing the work on the rifles. You guys may be more familiar with Jt depot markings, i.e. Ingolstadt (in German the J and I are interchangeable).
However, I don't believe that this carried over for the Luftwaffe, exactly. We do know that the Luftwaffe had individual repair depots known as Luftzeugamt. These Luftzeugamt would be responsible for repair of weapons/equipment. It's clear that these Kü marked Lugers have been through a depot, as they bear the Luftzeugamt eagles associated with them. With that in mind, i did some searching for possible Luftwaffe LZA facilities and found 1 perfect match:
Sagen-Küpper. Known as Küpper bei Sagen, but even better known locally as just "Küpper". So, armed with my working knowledge of the repair system used by the Germans, it seems very clear to me that the Kü marking is the marking of the Luftzuegamt repair depot at Sagen-Küpper.
The following PDF file contains info about the Sagen-Küpper airfield (P.585): http://www.ww2.dk/Airfields - Germany [1937 Borders].pdf
From that page under the History tab:
" History
: built in 1936.Luftzeugamt located there"
If this isn't the answer, I hope that my posting will cause some discussion that might lead to the answer, but I'm fairly certain that this is the answer we've all been looking for.
It's very buried if you try to Google it. You can search Kupper (without umlaut) and some more searches show up. Below is a workers badge from the Küpper LZA.
Hello fellow collectors. I believe I may have solved the mystery of the "Kü" marking. Background, some may know me some may not. I am active in the K98k collecting field and have co-authored a few books on the subject. We are working on Volume 2 in which I will cover the repair depots that repaired K98k's. In doing so I have acquired a bit of a feel for how the Germans marked depot weapons and such. For the Heer, the typical abbreviation for depots uses the first and last letter of the depot: for instance Spandau is shortened to Su, Mainz is Mz, Krakau is Kru, and these abbreviations were applied to the rifles in the way of inspection stamps to show the repair facility responsible to doing the work on the rifles. You guys may be more familiar with Jt depot markings, i.e. Ingolstadt (in German the J and I are interchangeable).
However, I don't believe that this carried over for the Luftwaffe, exactly. We do know that the Luftwaffe had individual repair depots known as Luftzeugamt. These Luftzeugamt would be responsible for repair of weapons/equipment. It's clear that these Kü marked Lugers have been through a depot, as they bear the Luftzeugamt eagles associated with them. With that in mind, i did some searching for possible Luftwaffe LZA facilities and found 1 perfect match:
Sagen-Küpper. Known as Küpper bei Sagen, but even better known locally as just "Küpper". So, armed with my working knowledge of the repair system used by the Germans, it seems very clear to me that the Kü marking is the marking of the Luftzuegamt repair depot at Sagen-Küpper.
The following PDF file contains info about the Sagen-Küpper airfield (P.585): http://www.ww2.dk/Airfields - Germany [1937 Borders].pdf
From that page under the History tab:
" History
: built in 1936.Luftzeugamt located there"
If this isn't the answer, I hope that my posting will cause some discussion that might lead to the answer, but I'm fairly certain that this is the answer we've all been looking for.
It's very buried if you try to Google it. You can search Kupper (without umlaut) and some more searches show up. Below is a workers badge from the Küpper LZA.
It makes perfect sense. They are struggling with the information you've dropped on them. That there would not be crossover in the analysis is bizarre to me, that they would never seek out the answer with the K98k side. Logically, the same small arms repair depots did the pistols, rifles, SMGs, etc. We've been discussing this issue for a long time, with Simson having devoted a good bit of time to it. Are they resistant to the information? Perhaps it's a bit of territorialism 
I don't see how they could have figured it out without branching out into our HZA info.
