. History/Background
the 1889 founded company „Rheinische Metallwaaren- und Maschinenfabrik Actiengesellschaft" (later renamed to Rheinmetall) was/is a defence company involved mostly in guns/grenades, but also in small arms. In 1901 Rheinmetall acquired the Dreyse company in Sömmerda. There, production of fuses, pistols, small bore rifles and ammunition was continued or set up. A known product from Sömmerda (a small town in Thuringia, Germany) is the Dreyse 1907 pistol in .32 acp.
After WWI Rheinmetall moved increasingly into non-military production; as a part of the newly discovered business the Rheinmetall Nr. shotgun was developed.
Development of the Rheinmetall Nr. 4
On 14. October 1919, German patent 358357 was applied. Said patent shows a shotgun looking very similar to the Browning A5, but having a fixed barrel and a rotating looking breech device. Obviously, it had a box magazine, not a tubular magazine.
On 27. February 1922 German patents 366337 (removable bolt handle) and 374071 (magazine cut-off) were filed. Both devices are present in the Rheinmetall No. 4 also.
Begin of sales: I assume, sales started in 1922, at least not before filing of the two latest patents in February 1922. In a book [Ref. 1] is stated, that “currently the Rheinmetall is working on an automatic shotgun, but it isn’t ready yet”.
End of sales: My guess (!): in 1926/27. In a book [Ref. 2] of 1926 the Rheinmetall No. 4 still is described thoroughly, but it isn’t shown in the Geco catalog of 1927. And in a book [Ref. 3] of 1928 is mentioned, that production of the Rheinmetall has been discontinued. As reasons is given, that the Rheinmetall wasn’t as handy and reliable as the Browning.
In any case: only very few ever were made. The exact number is unknown to me; even a ballpark figure strictly is a guess. I’m guessing (!) a total number of app. 5,000. Hopefully; I’ll be able to give a better figure in the future. All No. 4s were made in 16 ga with short 2 9/16" chambers. Three barrel lengths were available (Ref. 4) i. e. 65 cm (25.6"), 70 cm (27.5") and 74 cm (29"). All Stocks had a pistol grip and a cheek piece. Buttplate is horn without any factory logo. Only legend present is “Rheinmetall Nr. 4” on the left side of the receiver.
By the way: I don’t know, why it’s a “No. 4”. I’m not aware of a “Rheinmetall No. 1” No. 2, No. 3. Maybe (!) it’s the number of development projects. The one shown in the first mentioned patent could be the No. 1 - the last development was the No. 4. I don’t know. An other explanation could be, that Rheinmetall emphasized the 4th automatic shotgun. This may sound strange, but in the article of 1925 it is emphasized, that the Rheinmetall is, in fact, the fourth auto shotgun after the Browning, the Sjögren and the Winchester.