If your revolver has the remnant of red paint on the barrel, I strongly suspect it is one of the 20,000 .45 revolvers that were included in the 37 million dollar sale of artillery, ammunition and small arms, which the British government bought off the US Steel Company, the US government having sold the same day this equipment to the US Steel Co. This was to get around the US Neutrality Act which was in force at the time. This sale also included 500,000 Model 1917 rifles and 80,000 odd assorted machine guns as well as 500 .38 S&W revolves and 900 odd 75mm guns, etc.
My reaserch at the UK National Archives and American archives shows that, the contract was amended about 4 times and the total dollar value ended up being about $43 million, the final number of M1917 revolvers shipped was actually 20,100.
This was in July 1940 so well before Lend Lease, the guns were paid for by the British.
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Regards
AlanD
Sydney, Australia