1870’s for a few decades we probably qualified as said nation.
Probably not even then. The NRA was founded in 1871, to promote rifle marksmanship and safety. Some of the NRA founders stated how they were appalled at the state of marksmanship common in the US and felt a group to teach basics and advanced shooting was needed.
There was also a matter of national pride involved. We lost a prestigious match (Creedmore? Wimbleton? I forget and don't feel like looking it up) to I think the Irish, and that stung more than a few people's sense of propriety.
In one way, we were a nation of rifleman, at one time, with more of our people literally earning their living using a rifle, or some firearm, than other nations.
The patriots of 1775 all had smoothbores,...
Most, by a fair margin, but not all. There probably wasn't any number of actual rifles at Lexington or Concord, certainly none on the British side.
A couple years later, when the colonists fought the British in actual battles with formed military units, there were a few rifle equipped units, but the main infantry used muskets.
With the weapons in use at the time, the musket was the military arm, primarily because it allowed for a few (2, perhaps 3) rapid shots, and mounted the "real" weapon, the bayonet. Standard tactics was the formed unit (all those guys stupidly lined up in the open -which was because commanders aimed the fire of the unit,) giving the enemy a volley or two. and then closing to decide the issue with cold steel (the bayonet).
Rifles did not allow the mounting of a bayonet, and were slower to load per shot.
Lack of a bayonet put riflemen at a serious disadvantage when combat closed to hand to hand. Woodsmen with their rifles and farmers with their fowling pieces (which are essentially muskets that can't mount bayonets) were formed into units of their own, and by 1777 when we had some actual Continental "Regulars" tactics had been developed to use the riflemen and fowlers as skirmishers, primarily, and have the regulars (equipped with arms similar to the British) to stand and go toe to toe with the British. Didn't always work as planned, but that was the idea, anyway.