hmmmm in hunter safety they teach that guns with a hammer or less safe as many people will let the hammer slip while cocking it an kaboom.
judging from the number of people who did this in my kids class on a unloaded 30-30 while learning to handel the gun I see there point . the instructor was very adamant about how a lever action was a poor choice for a beginner .
I have put a zillion rounds through a lot of different over under guns shooting trap an never had a issue . I have seen one discharge at the line that might have been a gun closing on cocking .
id be more concerned about a hammer catching on some thing an then droping on a round to be honest. I have heard of this happening on revolvers with one iover the barrel as well as autos were it was not half cocked .