The statement "there are no drop in 1911 parts" is patently incorrect.
Operations to assemble the 1911 involve staking and fitting. That is gunsmith level work and those parts are not drop in. The plunger tube for one.
There are other histories of the Singer operation, and whether the 25,000 parts were meant to prove a point about assembly, it would seem a huge investment for the demonstration. It remains a fact that they were scrapped - not assembled. Why waste a signifcant resource? They did no meet inspection standards. Other historians have pointed out the parts were not acceptable and the rejection of that entire lot left only 500.
25,000 1911's is a significant loss and basically a failure on their part to demostrate how it SHOULD be done. Using the typical industrial value added method of costing parts sent to the next station for assembly, that was in todays dollars about a $10,000,000 loss. Having done something similar I well know how management views that. A batch of lost parts because the next station can't even cobble them together is a loss.
Goes to, the legend of Singer 1911's as being highly handcrafted yet they still couldn't do it, which is the reason for their collectibility and incredible values. But Singer and it's poor quality really isn't the story here. Its all about can you order parts from multiple sources and make a firearm with them? To my knowledge, you cannot just assemble a 1911 and expect it to perfectly function right off a kitchen table. I can't find any assembly instructions on line which promise that.
An AR15, yes, most of the time, with little problem. What does crop up are parts selected for their social provenance not their dynamic operation, and those rifles tend to have cycling issues. The main culprit is mismatched gas length and buffer weights, which is not readily understood by the beginner looking to make a gun that is visually impressive. Therein lies the cause of failure. Too many see the AR as a static manual action gun, when the reality is it cycles like an internal combustion engine. Correct selection of parts requires understanding timing of the cycle, dwell location of the gas port, and weight of the buffer/bolt carrier group assembly. How cool the parts are has no bearing any more than what color you choose for a carburetor. The jetting and air bleeds are much more important.
Singer fulfilled their contract, Remington and Ithaca proved the process worked with millions made. And a plunger tube isn't a drop in part.