Safety can be taken so far, then common sense has to take over. If a cap or flint hasn't been struck over the touch hole in twenty minutes or more, you shouldn't have to worry about the presence of glowing embers. But, for safety's sake, run your ramrod down the barrel and notice the position of your witness mark(s) indicating a loaded gun (you did remember to mark the ramrod didn't you?), if it shows powder and ball still in the chamber, use a worm to remove the ball and dump the powder. Now use your ramrod again, to check for another ball. When the chamber shows empty, per witness marks, it should be safe to use a bore scope.