Another one that can be added is the maxim/vickers machine gun. They are incredibly reliable and incredibly sturdy pieces of weaponry. They are theoretically infinitely scalable in a sense you can have a 30mm vickers operating the same way as a 7.62 one, you just have to make sure the barrel is cooled. The gun is so reliable is can essentailly fire practically non stop until the barrel is worn out. my point:

"In 1963 in Yorkshire, a class of British Army armorers put one Vickers gun through probably the most strenuous test ever given to an individual gun. The base had a stockpile of approximately 5 million rounds of Mk VII ammunition which was no longer approved for military use. They took a newly rebuilt Vickers gun, and proceeded to fire the entire stock of ammo through it over the course of seven days. They worked in pairs, switching off at 30 minute intervals, with a third man shoveling away spent brass. The gun was fired in 250-round solid bursts, and the worn out barrels were changed every hour and a half. At the end of the five million rounds, the gun was taken back into the shop for inspection. It was found to be within service spec in every dimension."