Mirikou over under... customer considered it "hard used" bought it in for missfires on the second barrel but we soon worked out it had had about 20 thousand cartridges through it... so i wouldn't have said hard used.
It didnt pop open on firing but the auto safety was linked to the underbolt... after a lot of mucking around trying to work out what was going on slow mo footage showed the underbolt was moving backwards a short way at speed enough to give the auto safety enough power to push the safety back... all springs were in good order and the gun was in otherwise good condition.
guns popping open really shouldn't be all that common. I would suggest that such an issue would be caused by lumps being knocked about and underbolts being refitted to damaged lumps. Any idiot with a hammer can make a gun "like a new one".. but it takes much more skill and work to make a gun "as good as a new one" and far more to do the work with subtlety
