A CAVIAT (or two): I don't like Rugers. I didn't like Rugers when I was still in business. I digress. There was a school of thought at one time .... one should do away with the Xfir Bar and add a Half Cock. This was done to provide a "catch" to prevent the speed burners in CAS from missing full cock and having to go "round the world" to pick up the unfired round. It worked ....... sorta.
First time I saw one of those guns I like'd to crapped my drawers. It (the half cock) wasn't a Half Cock Notch, it was a half cock LEDGE just like the full cock ledge. Were one loading away and spinning the cylinder to check for hight primers (very popular and flashy thing) and touched the trigger the hammer would fall (remember?? No Xfir Bar) and folks really thought that was OK.
I don't actually know how the Ruger mechanics are doing the deed this days (I haven't looked) and I don't much care (Remember?? I don't like Rugers) as I'm not really interested. No place to put the Caps.
So .... as above, and in partial response to Bibbyman, it is all too true any mechanical "system" devised by any overpaid engineers, can be defeated by determined individuals. Also, mechanical systems are also prone to failure. Murphy's Law ..... remember!!! Any in designed in mechanical safety requires one should use it. The Mechanically devised safety I like best is either a 10 stop 5 shot R & D type conversion cylinder or a 12 stop Colt pattern cylinder. Either must be mechanically engaged. Without design mechanical intervention, hammer down on empty chamber is the biz.
We must however, remain ever vigilant. It is a known factor, there is absolutely NO mechanical safety system, ever devised my man, that cannot be defeated by a determined IDIOT. so there.