There is no way to tell... however I believe the SS contracts were "built" in KL Gusen, and normal production at Steyr, with final testing done at Steyr - things to consider:
1. The manufacture of rifles start with fireproofing and end with testing, if they were made separately then it means KL Gusen would have had to have all the capabilities to fireproof actions (equipment and proofing ammunition). I do not know if that is the case, but they probably did as if they didn't the rifles would have had to go back and forth and that is not practical. Odds are they had the means to fireproof and the rifles were sent to Steyr for final testing only. I can't see extensive testing possible at KL Gusen, that would be problematic having complete rifles and large stores of ammo at a concentration camp.
2. Had testing been done, or practical, at KL Gusen, then after August 1944 they would have moved components and assembly to Gusen instead of moving assembly and testing to a newly built facility at Mölln, - they chose to instead keep them separate. It is also said "all" rifle assembly moved to Mölln late in 1944, this is probably why the SR stop, - by then the SS controlled all elements of the economy, - both Göring and Speer were marginalized; there was no longer a reason to manufacture for the SS independently.
3. SDP was a commercial concern, fully government owned but operated under Rheinmetall (also government owned) and theoretically for profit (
a meaningless concept in 1944 Germany). The military inspected their production on site but all procedures were done by company employees. It isn't like German soldiers were inspecting rifles, - so testing and dealing with commercial production would not have been a large burden, they would have to keep them separate (
SR and SS contract rifles exhibit low standards and my bet is they didn't meet Army standards) and the rune might have served that purpose to a degree.
Bottom line is I think rifles were probably all tested at Steyr but in the early stages, up to the August 1944 events, rifles were assembled at separate locations. The only direct evidence of this is company reported production numbers and the disparity in production ranges in “normal” (Army) observations, which suggests many more rifles were made than delivered to the military and Speers post war comments stating he was opposed to KL rifle assembly due to his inability to control the resources involved and disposition of the rifles (
which implies they were made in the KL system and went to non-Army users- the SS front line units would have been given quality rifles from Army sources, not the low quality rifles made outside of Army inspection.)
I cover this in my article, my thoughts, but the truth of it is there is little direct evidence before August 1944 and what we do know of KL Gusen's early operations come from holocaust researchers, the best from German holocaust authors (in German) and they are vague and often unreliable as they usually have an agenda (
they usually have a conclusion they want to "prove", rather than looking for information to form a conclusion...)
Do you think that the BNZ 43 & the BNZ 43 with the single rune came out of the same plant?