[Wonder Warthog]

Hmmmmm.....how about taking the Excalibur and fitting it with a second stage solid rocket booster. This wouldn't need to be terribly smart, as the needed guidance corrections for accuracy can be done after the stage separates from the round.

However, other than tradition, why is a "gun" needed at all, when the same job can be done by a much simpler guided missile??

[The Grammarian]

You’re kidding, right? Guided missiles are a lot more expensive than artillery rounds.