Hullo Michael . Yes , I always thought it was interesting the way the deficiencies of a single locking bar ; a tendency not to engage fully with the wheel slot and drop out formed the idea behind the two part sear and prop. Having said that in practice its often quite difficult to get the primary sear to disengage from the wheel unless the sear nose and slot are exactly the right shape. Too sloppy and the wheel doesn't lock off in the right place and you get problems with the pan cover link not keeping the pan shut properly . I don't think people always appreciate how tricky it was to get these all these things right.
And yes ; single locking bars do need a lot of effort to get them to disengage , hence a long or very hard trigger pull . So the cam or wedge type release system illustrated by Leonardo but seen on other locks does have something to recommend it .
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