I am glad you took the time to bring the rifle up for discussion, - I saw this late yesterday but didn't have the time to reply then.
The rifle is interesting, though you could show the stock better, does it have grips and are there any markings on the take down ferrule? The wrist acceptance is stamped so many times the original acceptance is indecipherable. Possibly a Danzig stock, but the acceptance under the cypher and lower are less reliable than the wrist. I guess it hardly matters though, from the looks of it this stock has lived the life of a floozy, it's been mated to a number of rifles before this receiver. None of the acceptance patterns are especially early though, no property marking I assume (left buttstock would carry the "1920" if it were in government hands early on, this alone would only indicate the stocks early status, but would help explain all the use it has seen)?
Best guess is this rifle was probably a black rifle brought out during the early rearmament phase, probably had been used in training (right wing militia / paramilitary working with the army in the east) and needed a new barrel. The rather early barrel and FP can be explained from this. The barrel is the neatest thing about the rifle, an early HZa Spandau made barrel, which means it was before 1935 probably, - because I believe Spandau worked with Spreewerke and they took over Spandau's barrel making operation. (Spreewerke in Berlin, - who seems to have worked closely with Deutsche Werke Spandau/HZa Spandau), I say this because HZa Spandau barrels seem to stop around the same time Spreewerke began in 1935, which happens to be the date Spreewerke came into being and took over former Spandau operations...). Not exactly especially relevant, but I know you are like I am regarding the industrial history behind the rifles.
I suspect the barrel was installed by HZa Spandau, probably in 1935 or so, the E/Su at the wrist a clue, then subsequently it passed through HZa Hannover (WW/Hr), a rather important HZa during this time frame. The two biggies 1923-1933 were at Spandau & Kassel (AK HQ for the Reichsheer), later Munich became important as did Hannover where an Army Acceptance Inspectorate was established (though don't ask me what they did exactly, - but sounds important doesn't it??). Later, certainly during the war, HZa Mainz (Wehrkries XII) passed it through, for what is anyone's guess.
Alternatively, it could be that this stock was on a different rifle until Mainz and that is where it was mated, - the sharp e/Mz8 and re-serial (countering stamping two or three prior serials) suggest it was just replacing the stock with a well used veteran of several ordnance repairs. If this were the case then the HZa Hannover would probably be for a different rifle and the e/Su just a coincidence with the barrel, but plausible because until 1926/27 the only reworking HZa operating were Spandau and Kassel, though Zeithain was building rifles from scraps as early as 1924, illegally of course, but the HZa's were illegal too, though the IAMCC knew about the HZa's (we know because they complained about them)
Yes, a lot of guessing involved with the rifle history, but I doubt we can be sure of a rifle with a stock that has been through so much! Typically the stock tells the story and this one has been around the block a time or two. I can only be sure of the barrel and the RR pattern suggests HZa Spandau, the counter acceptance stamps are common to Spandau work of the early rearmament phase, I think 1932-1935, which fits the period of the barrels manufacture (which was certainly not after 1935)
Lengthy - long winded - this is why I didn't reply yesterday as I didn't have half an hour or more when i saw the post.
