The bore is about 23" muzzle to vent, with powder chamber. Overall barrel casting is about 28". Wheels are about 30".
It is all cast iron; barrel, wheels, and carriage.
Does not appear to be sleeved.
Could be an older South Bend, but haven't seen one exactly like it on their site.
It looks like a cast iron carriage and barrel? If so, South Bend Replicas made and possibly still makes a similar all cast iron Howitzer. It has 19" diameter wheels and 19" long barrel. He may have made a larger version prior to these under the name Barney's cannons.