It is perhaps a stretch for me to say that free banking broke sound money, as a deleveraging event without a backstop can indeed happen and, if allowed to, you are still left with the bullion as total supply.
The issue is, while that's fine in theory, in practice, the inflated supply of credit that traded at par with money did have a devaluing impact on the money itself, as it of course had to. Just like a new deposit issued by JP Morgan increases the supply of dollars, despite the fact that the Fed didn't issue any new reserves, nor did the Treasury print any bills. Perhaps it's more accurate to say that the issuance of credit distorts, rather than breaks, sound money and its pricing in the market, but as far as the impact it has on the value in the marketplace, it seems to be a bit of hair splitting.