The Dahlgren guns were considered an improvement of the Paixhans, which could only fire shells (explosive projectiles) where the Dahlgren could fire shell, solid shot, and canister (lead ball anti-personnel) The Dahlgren guns had a characteristic shape, and SOME were rifled and SOME were larger than the Paixhans guns. Wikipedia has a good brief article on the Dahlgren guns, as well as Paixhans.
A Paixhans gun is an early naval gun for firing explosive shells.
Mainly in the stock
bronze and gun metal
Stock dimensions and sights
One barrel
A sub-machine gun fires pistol cartridges. A machine gun fires rifle rounds.
There is no difference in that either can be used for the other job. Of course there are hundreds of types of guns around in the building industry.
The Minigun is Gatling gun where the barrels are powered by an electric motor. The Gatling gun, was a hand cranked, multi-barreled gun.
none.
2mm in case length.
Stock and sights.
You have answered your own question.