I was always amazed that the New England gun manufacturers could turn out fairly precision products with relatively rudimentary, by today's standards, machinery.
Yes, New England was the heart of the Industrial Revolution in America. Oh, there were other places, such as Paterson NJ, and Ilion NY, but here in New England was where 'Yankee Ingenuity' made mass production of many products, not just firearms, possible.
However, it is a mistake to think that the machinery was crude.
Perhaps the most influential crucible of firearms mass production was the Robbins and Lawrence Armory built in Windsor Vermont in 1846. Techniques in mass production were devised there that were the basis for mass production of interchangeable parts for firearms for over 100 years. Today, the old Armory houses the American Precision Museum with a collection of some of the original equipment used to manufacture interchangeable parts for firearms.
Previously, many manufacturers relied on the English System of manufacturing. Highly skilled craftsmen would make guns and other products one at a time. What the Yankees realized was that using mass production and precision manufacturing equipment, less highly skilled workers could turn out interchangeable parts much more rapidly and economically than the old English Craftsmen. This became known as the American System. I visited the Precision Museum a number of years ago and took some interesting photographs.
This is a lock plate profiling machine. Rather than hand cutting the lock plate and filing it to shape, the plate would be rough cut slightly oversized, then fastened to the machine and shaped to final profile in one pass.
This machine was used to inlet the stock for the lock plate. The pattern shown was fastened to the machine. The operator manipulated handles to keep a stylus in contact with the pattern. The cutter was attached by a pantograph to the stylus and as the stylus traced the edges of the pattern, the cutter made the cuts in the stock to receive the lock plate. A relatively unskilled laborer could cut dozens of stocks this way in a fraction of the time it took a skilled craftsman to cut a similar shape in a stock using hammers and chisels.
A rifling machine.
This is how the rifling machine worked. Prior to this, gunsmiths would laboriously draw cutters through the bore of a rifle to cut the rifling. It took all day to rifle one barrel.
A stock duplicator. The pattern at the rear rotated at the same rate as the work piece at the front. The operator used handles to keep a stylus pressed against the pattern while a pantograph arrangement cut the stock. You can still buy duplicators like this from Sears, at least you used to be able to.
Another view of the stock duplicator.
Another profiling machine.
Don't think of this stuff as crude. Equipment like this could produce very precise parts, that needed little or no fitting to go together into a working firearm.
We are talking about the heyday of American Manufacturing here. Some of the men who worked at the Robbins and Lawrence Armory included B. Tyler Henry, Daniel Wesson, and Horace Smith. Henry went on to design the Henry rifle for Oliver Winchester in 1860, Smith and Wesson began manufacturing revolvers in 1857. Many of the techniques pioneered at Robbins and Lawrence were adopted by the Springfield Armory further down the Connecticut River. At the height of the Civil War, the Springfield Armory was able to produce as many as 1,000 rifled muskets per day.
By the time Colt, S&W, Winchester, and the others built their factories, many machines were dedicated to perform one operation only. A worker might spend all day producing the same part on one of these work stations. The machines were preset so that work pieces could be dropped in and the operator did not have to spend any time setting up the machine, parts could be manufactured quickly and precisely. The work flow was organized so that parts flowed from the huge hammer forges down to the smaller precision operations and on to the assemblers. Depending on the task, assemblers might be highly skilled at fitting parts, or the parts might go together with little fitting at all.
Anyway, long, long before modern CAD and CNC equipment existed, clever minds came up with clever ways to manufacture very precise parts and assemblies.