Well, the 1917 is, for all purposes, a hand ejector 2nd model chambered in .45ACP. The second model appeared in 1915 to simplify the triple-lock that was found too costly and unnecessary.
I read somewhere that it was the British, who bought a great many number in. 455, that asked the deletionn of the ejector rod shroud for fear of gumming up the revolvers in the muddy trenches.