Originally Posted by WoodenPlank
That much I am well aware of - I was more wondering about a rimless cartridge in a cylinder where you can't use moon clips that wrap into and around the shoulder of the rim. Are they headspacing on the case mouth, or what? If so, I'd imagine that cylinder has to be pretty carefully machined to keep the case from sliding forward without generating an over-pressure condition.
"Supposedly" with old wives tales, the first batches of Colt M1917 had .45LC cylinders and the rounds would fall all the way in. Note that I said "supposedly". I've never seen it in any Colt M1917 that I came across, including my own. Yes, they're headspaced at the case mouth and you can safely shoot, just that no extraction unless the rounds slide out - of which they do until the charge holes get too dirty then they'd start sticking. By then you either need to use moon clips or carry a pen/pencil and start poking out the casings.