The Gatling Gun underwent strenuous testing around the world:
The development of this type of weapon divided military men into two schools of thought. One believed that it should be an artillery support; the other considered it a special objectives gun for bridges or street defense. Neither recognized its true mission as an infantry weapon.
Many of the trials included its being fired in competition with howitzers and cannon. In each instance the Gatling placed more bullets in the target than did the artillery if allowed to fire as many bullets as the number of grapeshot fired. On the basis of these results, the gun was officially adopted by the United States Army on 24 August 1866.
[...]
Some of the European governments, in order to prove certain tactical points, subjected the weapons to most unusual competitive events. For instance, in Carlsbad, Baden, in 1869 there were pitted against the rifle-caliber Gatling, 100 picked infantry soldiers, armed with the celebrated needle gun and trained to fire by volley. The machine gun was to fire the same amount of ammunition as the 100 riflemen at a distance of 800 meters. The results showed that the Gatling put 88 percent of its bullets into the target, while the soldiers succeeded in scoring only 27 percent hits. Doubtless the difference would have been even greater had the firing taken place during the heat and smoke of battle.
[...]
The endurance of the Gatling gun seems almost phenomenal when judged by modern standards. On 23, 24, and 25 October 1873, at Fort Madison near Annapolis, Md., 100,000 rounds of center-fire caliber .50 ammunition were fired from one gun to test not only the durability of the 1865 model gun, but also the quality of the cartridges. Lt. Comdr. J. D. Marbin supervised these trials under the auspices of Commodore William Nicholson Jeffers, Chief of the Navy Bureau of Ordnance. Excerpts of the official report are given below:
October 23, 10:33 a. m., commenced firing in the presence of Chief of Bureau of Ordnance and others. Ten drums, each holding 400 cartridges (making 4,000), were fired rapidly, occupying in actual time of firing ten minutes and forty-eight seconds. The firing was then discontinued to witness experimental firing of the 15-inch Navy rifle. The firing of the Gatling gun was resumed in the afternoon, when some 28,000 cartridges were fired. Commenced firing at 8:50 a. m., October 24, the gun having been cleaned.
One hundred and fifty-nine drums, of 400 cartridges each, making a total of 63,600 cartridges, were fired without stopping to wipe out or clean the barrels. At the close of the firing, which extended over a period of five hours and fifty-seven minutes, although the actual time of firing was less than four hours, the barrels were not foul to any extent; in proof of which a very good target was made at 300 yards range before cleaning the barrels. On the 25th day of October the remainder of the 100,000 cartridges were fired. The working of the gun, throughout this severe trial was eminently satisfactory, no derangements of any importance whatever occurring.
100 picked soldiers against a Gatling gun. YES, the Gatling is superior. Tripod mounted and and even the same amount of rounds fired during the same time, accuracy of the gun is superior. Troops during the stress of combat their accuracy with the rifle even less than in a training or demonstration context.
Fouling of the Gatling gun a problem? Those weapons were still black powder and after firing a certain requisite amounts of rounds functioning of the weapon would become a problem?
Until recently you could buy a brand new brass Gatling gun for $30,000 USD. But the sole manufacturer has now retired?
“Ten drums, each holding 400 cartridges (making 4,000), were fired rapidly, occupying in actual time of firing ten minutes and forty-eight seconds.”
For reference, Todd Jarrett (a pro IPSC competitor) once shot 1000 rounds through a 1911 in the same amount of time (with the aid of a team of loaders).
Admittedly, he wasn’t concentrating much on aiming after the first few mags.