You are all wrong ... LOL!
The earliest 'inline' breech-loading fire locks date to the 1500s, like but this one example from the Royal Armory, however there are in reality 'custom' arms:
collections.royalarmouries.org
Commercially, I would argue that the 1st truly available black powdah inline was the flintlock Hall rifle, a breech-loading rifle that was patented in 1810 and fielded to US troops, from the Harpers Ferry Armory, in 1819. While the
French Chaumette inline breech loader dates from 1720 and the
English Ferguson rifle (Rev War era) dates from 1770 pre-date the Hall, those too are/were essentially custom items.
Unlike Eli Whitney, who all too often gets the credit for interchangeable parts, the parts for his cotton gins were only interchangeable from those built within the SAME batch. John Hall (Portland, ME) was a mechanical genius and not only invented the Hall breech-loading rifle, but all the means to produce it in quantity and where all parts were truly interchangeable. He invented the tooling, gauging and inspection gauges & systems, horizontal milling, drive wheel counter-weights to eliminate tool chatter (from the water-driven machinery), and most importantly - the micrometer as we still know it today - as well as the standardized/unified thread forms that we (the US) still use today. On my original flintlock Hall, I can replace any of the 10-32 threads with a modern machine screw and it fits perfectly!
During the acceptance trial of the Hall rifle at the US Military Trials, they tested 100 rifles and all passed all of the specifications and performance tests. Although he won the contract, to prove his machining methods and gauging/inspection ideas/patents, he then had all 100 taken apart and put into piles, with the parts all mixed up from which rifle they originated from. Then those supporting the tests reassembled all 100 of the rifles, taking a part randomly from each of the piles ... and one again all 200 passed all of the testing! And as things like this typically end up ... he himself reaped no financial reward from his many inventions, patented or not, and died a pauper ... whereas the military industrial complex garnered the glory ... and $$$!