Ony 300 that does make it intersting
Hi Images34: According to William H.D. Goddard's "The Government Models" your pistol number 31791 falls within the 300 pistols serial number range C24940-34619 shipped to the London Armoury Company on January 11, 1916. It looks like the barrel of your pistol has the London view/proof marks. Perhaps you can post more photos of your pistol to show details such as any other markings etc. You could also get a Colt Archives letter which might include more detailed shipping data ($100 and takes 2-3 months for reply).
Amazing these guns were side by side so long ago.