RENE lists 150-01128 as a "S" factory second SDA-32.
I believe that one and my #783 are the lowest SDA guns mentioned in RENE.
150-00783 shipped in June, 1971.
The subscription guns 150-00001 through 150-00200 were made later and I suspect they were all RDA-34 models. Many of those went un-purchased by their subscribers and were recently liquidated through CDNN. The 3 digit CDNN guns were all RDA-34's. The two lowest guns I have are #30 and #138, both RDA-34's (those were not in the CDNN load) and have characteristics of later manufacture.
But the fixed sight model was no afterthought, Ruger had it planned all along. The 1970 dealer price sheet shows both fixed and adjustable sight models in both .38 and .357 in all 3 barrel lengths (some of those 12 models may have never been produced).
The March, 1971 Shooting Times has a Skeeter Skelton review of the Security Six. ST got two test guns, an RDA-34 and an SDA-32. To make the March edition (which was likely at the presses in January), those guns would have had to have left Ruger in 1970 so were among the very first production guns. Though not noted, I suspect they were numbered in the 150-002xx range.
The July, 1971 Guns magazine featured an SDA-34 but again, no SN was mentioned in the article. I suspect it was also a 3 digit gun shipped no later than about March, 1971. Probably no higher than 150-003xx.
But the lowest SDA-34 that I am aware of is the serial number X2 prototype gun pictured in the 1970 Gun Digest. I don't know the configuration of X1, so at the moment I think X2 would be the answer to "How low can we go?".
