The 6 groove to 10 groove tang change is a good example of how a change order comes down at a certain date but sometimes happens at different times on different models not to mention that the completed guns were not shipped in numerical order but what appears to be what the employee had easy access to, my brain pictures the older guns at the bottom of the stack perhaps languishing there until a small restock or large order dipped into them but thats just speculation on my part.
Doc 44 had some interesting notes on some 10 groove tang 44 Magnuns shipping before some of the presumably older 6 groove tang ones but IIRC some of those 1956 10 groove examples actually had lower serial numbers than some 6 groove guns that shipped in 1957 but thats just from memory so will leave that up to his expertise to explain if true.
If true it is interesting.
In my mind the 6 groove 44 Magnums generally fade out in early 57, I used to think that the early Combat Magnuns had the 6 groove up to sometime below the K262000 like K26177x or something like that, but as an example in post 3 above we see a K262xxx CM reported as a 6 groove tang.
From my notes I see some 10 groove tang CMs in the K263xxx range shipping summer of 1956 so not a clear 1956 vs 1957 thing especially when comparing serials, tangs and ship dates on 44 Magnums vs .357 Combat Magnums.
