OK. Took a look at the number with more magnification/light; The bad news is that it is definitely 903806.
Looked in Clawson's book and Colt had numbers assigned between 856101-958100, but Ithaca also was assigned a block within that range at 856405-916404. A little confusing, but he also states that Colt made ca. 60,000 duplicate numbers in that range. That might explain the 903806.
Under high magnification/lighting, I tend to agree, now that I see it, that the right side logo is a rotary pantograph. When seen under 10x, the marks become obvious. Thanks for that observation, Bill deShivs.
Whoever did the welding to build up the breech face did a fantastic job. I can't see any pits or inclusions.
So, mystery solved. Someone wanted a 1911A1 in 9mm, and did a bang up job of modifying a garden variety 1943 Colt production slide to suit their purpose. I seriously doubt that someone was working on some special project; Just something a talented gunsmith did.
I had never really paid much attention to it as it was in a junk box of parts that I have had kicking around for along time.
I was a bit nonplussed when I saw it, as I was under that assumption that Colt had not made anything in 9mm until the 1950s at the earliest. At least now I know that it isn't some super-duper secret Colt project from WWII. LOL!
I'm with you about "rare & valuable," JimK. The one other time I posted (in another forum) something that I thought was odd and interesting
(NOT rare or exotic), I got all kinds of rude and accusatory posts in reply, implying that I was trying to pull a fast one. I haven't been back to that forum since.
Basically, that one was a gun built up by a base armorer for a Navy lieutenant in .22 cal. It was a Parkerized Service Ace on a Remington Rand frame that had what was one of the very last serials in the R-R 1945 range.
What made it interesting was that the letters "SM" had been very neatly stamped as a prefix to the s/n. There was no evidence that the "NO" prefix had ever been applied to it and certainly no evidence that it had been welded over. One so-called expert flat out said it was an altered number, and none of the frames came out of the factory without that "NO". Another said I was trying to perpetrate a fake, etc.
I made it as clear as I could that I thought the gun was neither rare, special or particularly valuable, only odd and interesting, hence my posts.
I was vindicated when I came across another very late Remington Rand on an R-R collector's website that clearly did NOT have a "NO" prefix for the s/n. So much for experts.
At any rate, I really appreciate the insights into these things. That's how we learn. Thanks, guys for all your observations.