In my collection of old American Rifleman magazines I have read that making shot pistols out of old US 1917 revolvers was a short lived craze in the late 40's early 50's. It would probably take me a while to find the actual articles but they were interesting enough that I haven't forgotten them. The revolvers were bored out smooth and shotshells were made up in shortened 06 brass allowing for a fairly decent shot load. By putting a small bottleneck in the brass they would headspace like a 45 or the chamber could be reamed straight and they could be used with moon clips depending on the users preference. Unfortunately the Feds decided they were in violation and put a stop to such goings on. Handgun length and smoothbore was not allowed, if they had left the rifling or added a shallow slow twist after reaming we might have had a Judge back then.
Confirming your memory, the Kent Bellah update of my 1965 edition of W.H.B. Smith's Book of Pistols and Revolvers - p 719 - shows a smooth bore Colt 1917 with a screw on choke tube made by famous wildcatter Jim Harvey.
Bellah cites Harvey as making them from 1952 until 1956, which is the date he gives for the ATF ruling. (ATFU then??)