Why squeeze-bore guns become harder to scale up

Does a 120 mm squeeze-bore gun show that a 6-inch naval version would be practical?

No; the increase in power and barrel wear makes the larger naval weapon a substantially different problem.

A proposed large squeeze-bore naval gun runs into the power of the shot and the resulting barrel wear. The existence of a 120 mm example does not establish that the same approach scales readily to 6 inches. The response stresses how much the power changes between those calibres.