It seems to me that you may have a 1917 Colt or a New Service. I seem to remember that these 1917's were made on the pattern New Service frames. Is it a 45 ACP or a 45 Colt? Every now and then you may run accross a 1917 that was chambered in 45 Colt. I have a New Service in 45 Colt that has the nice old world bluing on it. I can't remember if the Colt book, that was published a few years back, had info on the large frame DA 45's. I may be wrong and have been wrong before. Luck on your search.