Chain shot was a thing. Two cannonballs attached by a chain (or by a bar making the projectile look like a barbell) were used in naval combat to cut the rigging on the sails. They were fired out of a regular cannon and were one of several attempts to make attacking the rigging on ships more impactful.
I have no idea why they’d try a double barrel field gun for a solved problem. The ammo did have an issue where it caused damage to the barrel and was ridiculously inaccurate compared to ball shot, but I don’t see how this design solved that. The chain would have had to be six feet long at least for this gun and the ball would certainly run into it on the way out of the barrel.
I bet they wasted less money on this than the fabled Sgt. York M247. It was an experimental intelligent anti-aircraft gun that did things like lock targeting onto the spectator stand during the demo, or insisted that the latrine fan was a slow moving rotary aircraft.