"ISTR the Italian had an MG with oiled cartridges."
Oh dear god that brings back horrible memories.
"Gun-Grog.. "
Far better. But I'll settle for that.
"....(poor quality steel had been used which warmed up too much which in turn heated up the ammo and let cartridges ignite prematurely)."
Nope, if the firearm overheated top the point of cooking off rounde before they were even fired, the wood would be smoking and the shooter would be burning their hands! But your next sentence was accurate.
"...the cartridge casing was too long for the opening in the gun so that frequently the spent casings jammed the extraction port."
The distance between the shoulder of the casing (the bump before it narrows) and the chamber is called headspace. Too much head-space will allow expanding gases, burning powder, and bits of molten metal to fly back into the shooter's face.
Too little and you have a fast burning powder, with a solid object in front of it, with no where to go. Literally, a bomb.
"...as if all that wasnt enough, the overall workmanship of the fabrication of both weapon and ammo was very poor which added to the frequent malfunctions, jams and accidents..."
That about sums it up right there: Quality Supervision. Similar problem happened with 1903 Springfields, Rock Armory, etc. The workers thought they were experienced enough not to need thermometers while heat-treating the metal. Which resulted in the catostrophic failures of the Springfields, only 2 resulted in the deaths of the shooter.
One other thing that was overlooked was the open magazine for the Chauchat. That's just asking for disaster, and it's a HORRIBLE idea. Open spaces allow dust, dirt, grime, oil, and other objects to screw up the works.