Odds are fairly good Gusen is where a lot of these rifles were residing in May 1945, - it is known the US Army removed everything they could move before it was turned over to the Red Army (June-July 1945, - by a lucky coincidence SDP-Steyr, SDP-Graz fell in the US-English zones and although "captured" and looted by the Red Army between May and June 1945, the facilities were turned over to the US/English forces in June 1945. The Red Army got an empty Gusen... once it was realized the Red Army was looting Austrian facilities, the US Army did the same, subsequently turning over Gusen machinery to SDP, who in turn swapped some machines with a Polish delegation)
Naturally I think Mike is correct in his assessment of SDP and the SS contract, we spoke at length on this subject and it is a certainty that the SS contracts rolled over a number of times, the trends show this clearly. It is also obvious that the German Army was anything but thrilled with the entire programs SDP entered with the SS to manufacture rifles. Largely on the back of Army money. SDP was not owned by the SS, they were up to their eyeballs in debt to the LW and Army, technically they were "owned" by the Armaments Ministry and operated under the direction of Rhinemetall, another state owned operation (Georg Meindl thought he was John Wayne, he did damn well what he wanted.. with assbudies like Kaltenbrunner/Seyss-Inquart, fellow Austrian nazi assholes, who could blame him). Once the SS took over the Armaments Ministry, during Speer's illness this was irrelevant of course, but in the Spring of 1943 (when the SS contract was signed) it was a sore point for the German Army. I think it is beyond absurd to suggest the SS contract was destine to the front line units, a significant part of the rifles (junk quality, - the Army made a point to note these were made outside of Army inspection and therefore unsuited for military use) probably languished in SS depots or some police ordnance facility (there is a list of police depots longer than my arm...), what were used probably ended up at the KL's or police organizations, possibly some anti-partisan "half-soldiers/murderers", and a ridiculous few at the front near the end of the war. When the SS was in control and did damn well anything it wanted... a large number were probably in Poland, the SS "Disneyland" 1939-1945, where they murdered indiscriminately and indiscreetly, both at the extermination centers and the military factories (the Army ran munitions operations in Poland, largely with Jew and Pole labor, all ultimately at the discretion of the SS, who were not beyond a round up and shooting of workers if the Army annoyed them)
Such nastiness of the SS operations required rifles, the Army was never eager to supply them, the entire purpose of the 1943 contract was to satisfy this need, so it stands to reason the SS used these rifles to arm their executioner and police organizations (non-soldiers, - front line SS units would obviously be supplied by the Army). The fact that SS contract rifles survive in large numbers in essentially unused condition, or rather rifles showing little to any period use (what use they often show is post-1945 mishandling and abuse), far in excess of their SDP Army counterparts, speaks volumes in this regard
As for SDP-Walther, SDP was never a Walther, not after 1938 anyway, - the likes of G.B. Jarrett was eager to visit Walther, no such eagerness was shown at SDP operations. Molln after all was just some temporary barracks (shacks, wooden structures), a outhouse in the middle of nowhere... Walther is was in Z-M and nearby Suhl, also an industrial area of some importance. Anyway, I doubt any GI was eager to brag about capturing a bnz/45, he probably would have been prouder of strutting around some fat Austrian fräulein than a crappy bnz/45.
*** SDP was investigated by US Army ordnance teams, teams that were tasked with investigating unusual or innovative weapons. The team sent to SDP found nothing worth studying.