Got my Great Grandma's Iver & Johnson 32 black powder, but I will never shoot it. It does not lock up very well at all. Great Grandma used to sleep with it under her pillow.
From what I understand, if it tight (cylinder) then its ok, if not don't. I think mine freewheels unless I have the trigger pulled all the way, then it is very tight. But still give her a good cleaning, see if it can be repaired etc, and then you have an heirloom that WORKS. It is a nice thing to know that it would work if needed. I think they can be fixed cheaply, at least mine was if time did not count