I 3d print projectiles and they're very simple to reload. I can lob a lead payload projectile 200+ meters with hi-low pressure shells. It's $2 of plastic and lead over 8gr of 800x behind a copper burst disc. Very cheap to shoot. Many times the projectiles are recoverable.
I just need a decent rifled launcher to start having real fun. Right now I stabilize my projectiles with fins and a very heavy nose. Rifling would get me further, as I could make my projectile more aerodynamic and rely on centrifugal stabilization from rifling rather than the "mortar" like stabilization that comes from using the property of center of gravity well ahead of center of pressure.
In the US, a rifled gun over .50 is a DD, but in Canada, it's still a non-firearm. So 37mm rifled, 40mm rifled, no problem in Canada. Just no one makes them and sells them to civs