That picture is a bit of a red-herring. Though the patent for a MG mechanism may have been patented as early as 1870, the actual MG wasn't built then. The patent was taken out by Friberg but what you see is the 1907 MG built by Rudolf Henrik Kjellman using the patent design, and subsequent improvements in ammunition. So, Gatling was the first operational machine-gun.
Do my eyes deceive me or was that thing intended to be hefted up to the shoulder and fired as a conventional rifle? What do you suppose the business end of that thing weighs, 107 1/2 lbs? You'd need the recoil just to keep it up and not shoot the ground or your toes, the heck with keeping it on target.