I could always cock "IOne" hammer as quickly as I can push off a safety, quicker than any safety other than a tang safety. I have small hands though with a short thumb so do not feel safe trying to thumb back two at the same time. Consequently although I admire the beauty & lines of a good hammer double I have done the vast majority of my hunting with hammerless guns.
Safety is for the most part a matter of the shooter rather than the gun. I have to date never had a hammerless "Jar Off" though I do realize it has happened on occasion. I once while navigating a rather steep hillside stepped on a rock which rolled & I went down to the ground & slammed my hammerless Lefever real hard, it didn't go off.
Personally I will never carry a gun open except on a very limited basis. This might entail if should happen to meet another hunter/s I might open the gun as we approached out of courtesy. I can very easily had I taken the above described tumble with my gun broken open it could very easily have put a tremendous twisting strain on the barrel which could have caused severe damage. Something to think about. "IF" I have to navigate an area through which I consider it unsafe to do so with a loaded & closed gun, I unload & reclose the gun. When I get safely through the area I then reload.
The unexpected is of course what we have to take into account. The above instance of the rolling rock is an example. It occurred one day while I was trying to navigate into position to pot a squirrel for the pot & was intent on looking up in the tree. I generally squirrel hunted with a 22LR but on this particular day had carried the Lefever for some reason.
It did however reaffirm my belief that a Lefever is not particularly susceptible to jarring off with their top hung sears & that a gun is not near so susceptible to being damaged when closed as when open. Take all this for whatever its worth to you, it didn't cost you anything.
