I have not been able to trace any reference to this adjusting screw mechanism prior to 1946, and I strongly suspect that, whilst several of these sear engagement adjusting screws are known to exist on Zischang Borchardts, they were fitted long after the Master had passed on.Harry
I have Mr. Niedner's Borchardt in caliber .38-72 with a Stevens-Pope barrel that dates to circa 1906. Tom Shelhamer had this rifle with the tools for sale in August of 1925 and it has the adjustment screw. I have no way to know when it did sell.
I feel confident that it's the work of Mr. Niedner but don't know when it was done.
Although the rifle came with the original Niedner mould and breech-seater I don't think it was shot much or any at all. The person I got it from or the one before him did not want all the paperwork that came with it and told that person to keep it and I've never found him.
I would be surprised to find an adjustment screw on a Zischang with DST's. Does the rifle pictured have DST's?
The .38-72 Pope is next to the Maynard Long Range.
