The Gatling is pretty reliable inherently. Dud primers just mean the mechanism yanks the faulty cartridge out and dumps it in the pile of fired casings. Accles put on demonstrations for the US Navy in 1898 with 100% reliability.
That still gets me, by the way. One of the big military problems at the time that was of interest to naval powers was torpedoes–this was before submarines, back when torpedo launchers were normally found as part of coast artillery installations. Torpedoes of that era were short-ranged and ran very shallow in the water, so that a guy back at the launcher could steer them through a cable, sort of like a predecessor of the wire-guided antitank missile. Lots of big expensive dreadnoughts were built with lots of small and medium caliber high-rate-of-fire “anti torpedo guns,” everything from belt-fed MGs to 3” guns, intended to stop incoming torpedoes by either blowing them out of the water with high explosive shells or by putting a wall of metal between the ship and the torpedo–conceptually similar to late 20th Century CIWS. I wonder if Accles had said “you guys are worried about torpedoes, right? How does a hundred rounds a second of rifle caliber bullets sound to you as a countermeasure?” history would have gone differently. Electric Gatling guns would have added to the horrors of trench warfare, I suppose. I doubt it would have deterred the French general staff or French politicians. I put the chief blame of World War I on French jingoism and desire for revenge for the thrashing the Germans gave them in the Franco-Prussian War. Had the French not been so butthurt and so eager for a rematch, the war might have remained regional, or not happened at all.
But I digress. There were public demonstrations of the Maxim Gun in the UK in the 1890s in which one gun fired over 150,000 rounds a day for a week during daylight hours with no breaks except to reload it and put more water into the barrel jacket. It expended over one million rounds of .303 rifle ammunition with zero malfunctions other than a few cartridges that failed to fire due to faulty primers. Not one failure to feed, not one failure to extract, not one failure to eject, this with a Victorian Era design that used strips of cloth to feed it instead of a modern linked belt.
A lot of the Victorian era tech worked just fine. It was, by the standards of 130 years in the future, heavy, expensive, mechanically more complex than it needed to be, full of expensive parts that had to be manufactured as milled steel forgings and hand fitted, and often required a second crew member to sit there feed the cloth belt of ammo into it by hand to keep it from twisting and misfeeding–but that was okay, he was an extra pair of hands when it was time to reload or pour more water into the barrel jacket. But it worked just fine.
One of John Moses Browning’s toolroom prototype M1911s at the Army trials in 1910 fired six thousand rounds in one day with zero failures to fire or stoppages of any kind and zero parts breakage–not stopping to clean or lubricate it, and dunking it into a barrel of rain water whenever it became too hot to hold, then shaking the water out of it and continuing to shoot. Another prototype M1911 fired eighteen thousand rounds over the course of several days with the sole malfunctions resulting from dud primers or deliberately damaged, crumpled cartridges that would not fit into the chamber, with, again, no parts breakage. This with whale oil and lard as lubricants–only applied before the test began. That’s better than some current production HKs do–in 2010 the guys at pistol-training.com did a 10,000 round torture test of an HK P30 in 9mm and had at the end broken no fewer than seven (7) parts, though to be fair none of them shut down the gun completely, they just caused problems with things like the decocker, or the mag catch.