My information on the ownership of the S&B Schönebeck factory from WW1-WW2 is collated from a number of sources and is s bit more detailed:
*During WW1 in 1916, shares in this company were taken over by Steyr-Werke AG, Wien. After WW1, S&B never regained control of the Schönebeck factory and S&B sold the factory (buildings and remaining shares) completely in 1921. In 1922 it became a branch office of the Oesterreichische Waffenfabriks-Gesellschaft (Austrian Waffenfabrik AG). *
*In 1926 it was briefly owned by HIRTENBERGER PATRONEN before it became a branch office of the STEYR-WERKE AG in Vienna and was known as “Zündhütchen- u. Patronenfabrik vorm. Sellier & Bellot, Schönebeck a. Elbe, Inhalber Steyr Werke AG i. Wien” *
By 1929 it produced a range of ammunition, detonators and electrical igniters. It appears to have generally used an “SB” hs but a "STEYR * 8,2 x 56 * " (A48) hs may well have been produced during that period.
*The ownership changed again in 1930, as the shares and the factory were taken over again by the Hirtenberger Patronen-Zündhütchen + Metallwarenfabrik. *
In 1933 all shares were back in the hands of 2 German firms again: The Dynamit AG (vormals Alfred Nobel & Co, Troisdorf) and the Rheinmetall-Borsig AG Duesseldorf+Berlin. The name “Patronen, Zündhütchen- und Metallwarenfabrik A.-G., vormals Sellier & Bellot, Schönebeck” is known from a price list dated 1936. So, the “Metallwarenfabrik” did not become part of the name until after 1931 and before 1936.