Gearing down was a long term survival strategy recommended by the technical advisers to the Emergency Committee Cabinet and adopted by the whole Grantville Emergency Committee (GEC) and the successor government of the New United States as the best way forward to ensure maintaining as much technology as possible and keeping a technological edge over the many international powers active in Europe. In two words, the immediate impact can be described as "Steam Engine".
Some 20th century technology simply could not be maintained or manufactured any time soon in the 1600s, and was thus out of reach. By gearing down, which became something of a mantra and motto, the town citizens meant to plan ahead and use the assets such as up-time machine shops and the power plant to create a sustainable 19th century technology base, in anticipation of parts wearing out, failing, or normal breakage. In general, the philosophy was to create a technology more advanced than any in other European nations, to maintain an edge and naturally promote business opportunities, since wealth was closely tied to national security capabilities. The GEC aimed not to maintain a fleet of motor vehicles, which contain thousands of parts and dozens or hundreds which require special tooling they need the machines to make the machines to make, but instead use the tech base to establish the railways and more advanced canals typical after long years of nineteenth century development.
In terms of personal weaponry, instead of attempting modern repeating automatic rifles, the strategy was to equip a professional army with a long range flintlock capable of three shots per minute and of outdoing any firearms in enemy hands in rate of fire, range and accuracy. The strategy anticipated an eventual gearing up by conversion to a breech-loading percussion cap or bolt action, or other advanced designs as other dependent technological factors were resolved to support the higher technology. The bottle neck of production was that Grantville had to build a whole industrial chemical complex as well as specialized tooling, which was a reason for not producing modern propellants and staying with black powder weapons for a few years. The crucial difference in what was producible outside the five advanced machine shops with perhaps a strategic assist in making a specialized tool from the machine shops—which are therefore operated in a manner to preserve their ability to assist—to make the tools that make the produced artifacts, while concurrently not acting without forethought "in the moment" to overuse irreplaceable tooling so that it wears out prematurely.
Certain aspects of this approach did underestimate the intelligence of 17th century inhabitants: France was able to adapt up-time ideas to build breech-loading percussion-cap rifles by 1634.