Firstly your questions:
I think it is clear from the DWM cartridge drawings that they were designed BY or FOR W. Förster of Berlin.
******************** Notes on 9x74R are brief - not produced or mentioned anywhere else (than DWM references) to my knowledge:
The rare 9x74R was effectively the prototype for the slightly later and much more popular 9.3x74R Mauser (M60). This was the first of several calibres introduced/designed by/for W.Förster/DWM and intended for single shot drop barrel, drilling’s, double barrel and combination rifles. They were all of greater than 70mm case length and some are still popular today, especially the 9.3x74R Mauser (M60). This case is the longest sporting calibre of 9mm. The 8x75R Behrs (M62/63) and 7x75R Vom Hofe (W31) were both based on this case type.
However, the 9mm type was short-lived being only produced by DWM with “DWM K 474 K” hs. Case #474 was introduced c1900 but it was not listed in the 1904 catalog. Förster obviously felt that it needed a slightly larger calibre bullet and so it was soon replaced by the 9.3x74R Mauser about 1902.
In Buttweiler VII/2 #205 it is stated that “… reportedly less than ten of these cases were found with original bullets some ten years ago (ed. ie c1980)… With only one factory loaded example believed to exist…” This information is unconfirmed but this is certainly a rare cartridge.
***************Some notes on the 9.3x74R
This very popular cartridge was introduced c1902, being produced by most European ammunition companies. In 2004, it was still currently listed by RWS, Norma and SBP. This cartridge was most widely used in double rifles and was superior to the 9.3x72R Express (EXP17), which it effectively superseded as the most popular cartridge for that purpose.
Dr Manfred Rosenberger in his ‘Cartridge Guide : II/71’ stated re the 9.3x74R:
“This cartridge, widely used in Europe, was originated in Germany about 1903 as a competitor to the .400/350 Rigby and the .400/360 Purdey. It was made from shortened and necked down .400 3 1/4” Express brass. It appeared on the market under the designation 9.3x74.5R. After the normalisation of case measurements of 1905 it got the final name 9.3x74R Mauser."
Whilst most of the above appears true, some aspects I don’t agree with. Rosenberger refers to the ‘9.3x74.5R’ as being the first version of this cartridge and he was obviously referring to the RWS version with “R.W.S.-N 74.5–9,3” hs. In the DWM casebook it is clear that the 9.3x74R (DWM case #474A) evolved from the 9x74R (DWM case #474 c1900 see M59). Both were listed for W.Förster of Berlin and are very likely to have preceeded RWS production. Note also that the earliest RWS catalog that this was listed in was the 1912 catalog (not shown in a c1900 catalog) and it is shown by RWS with a “No 474A/9.3mm” designation. RWS appears not to have shown DWM case numbers in catalogs if RWS had introduced the cartridge - only if DWM introduced the cartridge and it was generally known in the market with that title. DWM first listed this cartridge in their 1904 catalog.
Comparison of RWS case drawings and RWS examples show that the early “R.W.S.-N. 74.5-9.3” does appear to have minor case differerances but it does however appear interchangeable and not a unique calibre. The pre-normalised form has a 0.5mm longer case at 74.7mm but all other dimensions are the same as the normalised form. The 9.3x74R was not shown in ‘Normalised lists’ until 1913 and the earliest of such lists was evidently promulgated in 1909.
The so called “9.3x74R Mauser Magnum” with an “RWS 9,3x74R MAG” hs (M82), was more than just a more powerful loading of the standard 9.3x74R. It has a 0.5mm larger rim diameter and is unlikely to be suitable for older weapons. Use of the H-Mantel bullet was in the 1934-1940 period which is believed to be the period when the “Magnum” loading was produced.