Just read your response a second time. Didn’t you know that the HARP barrel was reamed to be a smoothbore? There was never any reason to make system “accurate”: it was designed to fire almost vertically to attain the highest possible altitude, not to hit some target on the ground.
The HARP sent a 400 pound projectile to an altitude of 110 miles - hardly a Mickey Mouse operation!
The project was cancelled more because of friction between Canada and our government over Vietnam than by the insidious machinations of the Missile Lobby.
I never said it was Mickey Mouse, just that it was done on a shoestring by comparison with most projects.
And, I did know that the HARP barrel was reamed to a smoothbore. OTOH, the M1A2 (and predecessor versions) Abrams Tank has a 120 mm smoothbore main gun, and it is no slouch for accuracy. Smoothbore is not necessarily inaccurate, and always produces higher velocity than a rifled barrel under the same conditions.
I do recognize that artillery is different than an armor piercing round at much shorter ranges, but I think the real difference between Bull's results and the 120 mm smoothbores is the development funds expended.