You are correct in assuming the shoulder in the chamber is there for headspacing purposes. However, since SAAMI sets the specs for cartridge dimensions, the shoulder is placed at maximum case length depth for a given caliber. My experience has been that any factory ammo or brass, when new, is always considerably less than this dimension - meaning that, in reality, headspacing on that shoulder, by the case mouth, seldom actually occurs.

With a semi-auto, the reality is that the cartridge headspaces on the extractor - not the shoulder in the chamber. With your single action Rugers, since extraction isn't a problem and you have a rebounding firing pin, it is just made long enough so that, even if the hammer blow drives the cartridge into the chamber, the FP is long enough to still cause ignition.

In instances like your 610 or M1917, what does happen is that variances in chamber roundness, smoothness, cleanliness and other variables, will hold some cartridges firmly enough that a firing pin strike will ignite the primers. Others are driven forward in the chamber, which results in a light primer strike and a failure to ignite.

Just as some rounds are held tightly enough for ignition and others are driven forward, some cases may drop out of the cylinder from gravity, while others may be "pluckable" and yet others will have to be poked out using a rod.

You should consider moon clips essential for any revolver that is chambered for a rimless or semi-rimmed round. The other alternative is using the rimmed version of that round, if one exists.

Moon clips are the greatest thing since sliced bread and your aversion to them is, most likely, founded in falsehoods found on the Internet or from people who either have no personal experience, or just a passing experience with them.

In order to fully utilize, and fully enjoy, them requires the right tool(s) to load and unload the clips.

Adios,

Pizza Bob

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