Stan, I agree the differences may be academic in practice, as are many of the differences between back and bar action locks. I assume you have read Burrard on the matter so I won't re-hash the stuff you already know.
It is a fact that the British gun trade used coil springs as a cost saving measure in general. I cannot think of a single long-lived really top quality gun made with leaf main-springs, though some makers did experiment with them (Greener & Scott spring to mind) and ultimately rejected them for their best models. Maybe others can come up with an example. I'm not being dogmatic about this, just observational. Coil springs did persist in lower grade models.
In my experience, where one mainspring spring is significantly different in power to the one on the opposite lock, it is because one has been replaced at some point in the past.
Almost all the quality hammer guns I pick up, ant they number hundreds per year, demonstrate that well made leaf springs are as good a century after they were made as the day they left the workshop.
The finest triggers in the world employ coil springs - really? Somebody please tell the British shotgun makers, they missed that.
It does not really matter does it? I guess the observation that leaf springs are preferred in quality British guns is the essence of the discussion on them, whether you think they got it right is something you are welcome to argue.
