The info on the "RSQ" powder came from several sources, and I honestly don't know which is correct. But I am inclined to believe the story as I told it, partly because it has the ring of truth. The story that Maj. Casey named the powder seems unlikely, as DuPont named its own powders. But the idea that Casey produced a pun on the word "rescue" seems quite likely; contacts of the military and contractors in those days were less stiff and formal than today.
The cartridge problem is a bit murky. The Model 1909 revolver was adopted simply because the old .38s were not powerful enough and the Model 1878 Colt DA was both obsolete and not really suitable for military service. And no one knew when (if ever) the "pie in the sky" auto pistol would be good enough for adoption.
So, adopting the New Service in .45 Colt was a quite reasonable measure. Some experts believe it was intended as a stop-gap for a few years and only purchased, not adopted. But it was given a government Model number (which the Colt 1878 never was) and holsters were made for it. The Army might have intended to use the 1906 cartridge, but it had the same rim diameter as the .45 Colt, and trials of the new revolver showed that the extractor jumped the rims of the .45 Colt; the Model 1906, with a shorter case, would have been worse.
The intention at first was to design a cartridge that could be used in both the M1909 revolver and the SAA and DAA. That round was first loaded with 4.5 grains of Bullseye but any attempt to increase the powder charge resulted in high pressures. That cartridge was called the Model 1909 but was loaded only until April of that year. In March, a new drawing was produced increasing the rim diameter to .536"-.540", which meant that the extraction problem was solved but the new round (still called the Model 1909 cartridge) could be loaded in the SAA and 1878 only in every other chamber. That is the cartridge usually called the Model 1909 cartridge loaded with RSQ powder; it was loaded by FA at least until 1913 and some Model 1909 revolvers were in service until well after WWI, though it is likely none were send to combat areas because supplying ammunition would have meant another .45 cartridge in the overseas supply system. (The Model 1909 cartridge was never loaded commercially or on contract, only by Frankford Arsenal.)
Jim