Gentlemen,
The issue here is not when the dog works conveniently but when things don't run smoothly. As first noted by Fernando K and later by Philip, the dog catch, not working under spring tension, depends on 'harmony' factors, like being too tight or too loose and all that. As that Spanish author recalled, and brought to my own wording, it might not circumstancialy be in the mood to fully cooperate with the firing action. I relize that, holding the gun upwards helps 'convincing' the dog to easier disengage, for reasons connected to gravity.
Well Philip, i know the easy way to engage and disengage the dog catch but, i can't do it properly by my own, left handed i am ... you know
