Solid ammunition has never become obsolete for artillery - it's been continually refined to produce modern armour piercing ammunition.

Cannonballs became obselete not because they were solid but because they were incredibly aerodynamic. As another user mentioned, Sabot shells and most armor piercing shells are solid. In fact tanks that use the 120mm Rheinmetall tank cannon (specificnmodel escapes me) still use solid sabot rounds with a smoothbore barrel.

A smaller example however would be shotgun slugs.