I have added new images of the rifle.
We have identified Mauser as the source of the project based on input from Jon Speed.
Here is a copy of the correspondence between Nathaniel and Dr. Storz and Jon Speed.
I have also attached two drawings that Nate created detailing the unique rifling and cartridge dimensions.
Hello Dr. Storz and Jon,
Bruce brought to my shop today a very interesting rifle. Bruce and I gauged the barrel, did a chamber cast, and a general look over the action. The rifle is built on an unmarked Mauser action, which appears to have all of the developments matching a Turkish Model 1887. The rifle bears all the hallmarks of a Prototype/Test rifle, lacking technical stamping, acceptance marks, and even sight graduations.
Dr. Storz, this rifle matches very closely, but not exactly, with the rifle you show in your book on Gewehr 1888's on page 36 and 37. I thought it would be prudent to include you in the conversation in hopes that you may be able to offer some more insight, or even direction if other material may be available for research in the Bayern archive. If possible, I would be very interested to hear your insight, if any of the examples available to you match or are similar to this example.
Jon, I made up drawings of both the barrel and cartridge case for you as I thought you would find them interesting. The rifling is spectacular and fascinating. The relevant data is a 7.95 bore, 8.23 groove diameter, 228mm twist, and has 12 grooves!!!
I have been through both of my DWM books and have not found a directly comparable cartridge case. I have found several that are similar, but I am stymied by the 14mm base and 15mm rim diameter. I suspect that there is a disconnect here as this does not seem appropriate. Bruce just sent over the attached picture of the bolt face which shows this cartridge would not have had the 71/84 base. That skews the numbers on my Case drawing slightly.
A very interesting rifle, thanks Bruce for the opportunity! Dr. Storz, we appreciate any insight or input that you are able to offer, thank you! Jon, I look forward to hearing your thoughts and discussing this one at length!
Take care,
Nathaniel Myers