I believe this niche is today filled by mortar rounds, John. Plus there are virtually no instances of large formations on modern battlefields.
Sorry to b unclear. I was referring to civilian ownership in the US. Many seem very excited about $20,000 transferable LMGs that have a cyclic rate of $75/minute.
How to make a cannon at home
Making canister shot can't be that difficult. Filled with 000 Buck. Thats is some SERIOUS firepower.
No NFA paperwork or restrictions. 1/20th the price. Sure the thing is heavy, but you can buy an ATV to drive it around with your savings. Or a Gator. Or a used pick-up.
If you really want to go at it you could design an inline muzzle loading cannon with modern steel. Could probably cut off a lot of weight that way. That might be a little more complicated legally.