Even your steel ramrod is usually made of a softer steel than the breech plug in the barrel, so it should not do much, if any damage at all. The Brass fittings we use on traditional MLers- not military replicas-- are much softer than the steel barrels and plugs. No damage at all. I have seen some hickory rods with so much of a bend in their shafts that they can't be thrown down the barrel to " Ping" the plug as you describe. Our Range officers( in charge of safety) use a metal range rod to check those member's guns.
Basically, your " test" is a short-cut. The best way to know that there is NO powder charge or ball/bullet in the barrel, is to put a ramrod down the barrel. Mark it with your thumb at the muzzle, then remove it and lay it down alongside the barrel. The nose of the rod should be along side or behind the TH in a flintlock, or near the nipple in a percussion gun.
It takes quite a bit of practice for some people to learn the difference in sound from tapping steel to tapping soft lead. Those shooters who are TONE DEAF cannot do this at all. There are so many variables in creating a " bouncing Ramrod" that comparing the height of the " bounce" is meaningless in most guns, IMHO. :thumbsup: