Volley gun
The Ribauldequin was a medieval version of the volley gun. It had its barrels set up in parallel. This early version was first employed during the Hundred Years' War by the army of Edward III of England, in 1339. Later on, the late Swiss army employed it.
Colt House Revolver
The Colt House Revolver (also called, in its alternate 4-round capacity model, the Cloverleaf) was one of the first metallic cartridge rear-loading revolvers to be produced by the Colt's Patent Fire Arms Manufacturing Company, back in 1871. The same year, Colt's also patented the Colt Open Top, another metallic cartridge rear-loader, but in fact the Open Top production didn't start until 1872, although a pocket version of the Open Top, a completely different design, went on sales as of 1871, the Colt Open Top Pocket Model Revolver.