Measured length of 625-6 cylinder with factory S&B 230 fmj against the ledge = 1.616 in. Measured length with same round in 1/2 moon clip = 1.627. Brass of factory round =.891 in.
Measured this with one of the S&W revolvers owned, used and reloading for. Granted not all revolvers will measure exactly the same. Most S&W 45 acp revolvers were designed so factory rounds could be used without clips, but were designed to be used with the clips. Seem to remember S&W at some point actually putting out some without the stepped cylinder as a cost cutting move.
45 acp brass generally shortens up with resizing, and very likely won't headspace off the step in the cylinder, unless you do not use the clip. Even if the brass in the above example was at max length, it still would headspace off the clip (unless you didn't use one).
Even in autos, if your brass is short enough the round can headspace off the extractor. Please notice I said "can", not always or what it was designed for.
Interesting exercise is to measure length of some 45 acp brass reloaded multiple times using standard 45 acp sizing die.
When reloading standard 45 acp brass, am using taper crimp so round can easily be used in semi or revolver. When reloading specifically for revolver using AR brass, am using a roll crimp for the bullets with cannelure. Especially with Rem brass.