Please ignore Bob Taylor's response.
Quite a few years ago there were two closely related discussions about Armed Guard sidearms, at https://members.boardhost.com/armedguard/msg/1341627196.html and https://members.boardhost.com/armedguard/msg/1341063055.html. One comment offered by myself was quite uninformed, as it turned out, but others gave better answers. And other comments were completely off the mark. There were comments about Colt sidearms but not to the detail you may hope for. Regrettably, all of the persons who offered comments to those two threads have passed on, other than myself, and I'm not a veteran.
There is an Armed Guard Facebook group, which is public, so you are welcome to post your question there and see what response you get. https://www.facebook.com/groups/715188522376466.
Ron Carlson, Webmaster
Armed Guard / Merchant Marine website