Ideas keep coming around as discussed in another current thread. Sometimes the technology becomes available to make them practical.
Did Germany or the Soviet Union ever take them into the test phase, or perhaps into field testing???
The one I saw was interesting because it was a cylindrical projectile with cavities carved inside the bore filled with solid propellant. The nose shock wave was swallowed and oblique shocks reflected down the bore retaining supersonic flow down the bore, in part by the shock waves igniting the propellant. It was one approach to a supersonic combustion ramjet, but I don’t know if it ever achieved supersonic combustion. I don’t think the concept got beyond wind tunnel testing.