A Sims-Dudley Dynamite gun. In the brief period between the end of the C19 and the advent of the QF field guns of WW1 this used a smokeless powder charge to compress air in the lower chamber which propelled the main charge in the upper. It fired finned cylindrical nitrocellulose based 5lb charges up to an effective range of 900yards. They were sometimes referred to as 'aerial torpedoes'. Unlike 'proper' shells, the ammunition could be MacGyvered using black powder, blasting dynamite and a bit of sheet metal working. That made it popular with the insurgents. The US army had 16. Roosevelt and the 'Rough Riders' used one but they were soon rendered obsolete by 'proper' artillery with hydraulic recoil, one piece ammo and all the bells and whistles.