Bruce,
Is this the m you are referring to?
I think the sub-contractor field is something that will take extensive documentation and research to further identify and nail down.
Jon may be the only one that can speak to this from documentation, but what examples do we have of known suppliers supplying a certain part that we can then correlate to a part marking? Pre K98k examples that is.
To use the commonly seen "S" marked parts that are associated with Mauser. They are commonly found on Mauser rifles, but are found on other contracts/countries rifles as well. Most notably, large quantities of Mexican 1910 rifles have S marked triggers and safeties, identical to those found on Mauser produced rifles. Recent research has shown that Mexico never achieved domestic production for the 1910 (in production through 1934 if memory serves) and purchased large quantities of parts, which it then assembled into rifles.
Were these S marked triggers and safeties contracted from Mauser by the Mexican government in the 20's and 30's? Were they left over components from Pre WWI that were obtained through ??? channels by Mexico?
Fun fact, S marked triggers and safeties appear on Mauser rifles dating back to 1891!
I spend a lot of time looking at parts, and Mauser made parts have a dizzying amount of variety in parts markings. Even in the same model/component. In addition to S there are H, F, K, C, L, M, T, G, J, and then there are the Fraktur fonts and then the stylized fonts and then the "I don't know what's". (Like the stamp that looks similar to the Pillars of Gediminas on parts that were made by Mauser but clearly were not for Lithuania) Possibly Mauser reusing old stamps (which they must have had thousands of) from previous contracts for different work groups/masters/cells.
I've recently been tracking a fraktur U which shows on Mauser parts from early 1900's to the Standard Modells.
And if the marks are subcontractors, which they might be, then a PROLIFIC number of parts would have been provided by subcontractors. The fraktur S, Crazy S, canted S, and others that are often associated with Sauer, would mean, Sauer provided TONS of parts to Mauser, including receivers for several large contracts, commercial rifles, etc.
When I maintained dies for a Allison part, the parts were not marked A for Allison, why would Allison want their own parts marked? Nor were they marked for the company I worked for. When I was running them they had a K stamp, which the part was on Revision K, and a nonsensical date code system. Some of the letters could be design revisions. They could be date codes for production. Or as mentioned before work groups/masters/cells.
The common opinion that they are simply inspection/process markings may have some merit. I am working on 100 some pages of inspection for the Gewehr 98, but I have yet to see on any of the process steps mark, stamp, etc. Nor do any of the gauges seem to correlate.
Just food for thought