[@Dinh AaronMk]Actually, rifling itself was not really difficult to make. It did take extra effort but the most pressing issue was that rifling made it more difficult for muzzle loaders to be used. Breech locking mechanisms on the other hand required industrial rigors Europe was not yet ready to do on large scale. Though if Europe weren't busy with Napoleon you can bet that rifle technology would've been introduced in large scale decades prior. This is demonstrated the best with the fact that caplock muskets became obsolete almost in the same few years they were introduced. Though to be fair early rifles were more finicky so in a sense it was good for them to mature before moving on. Rifled muskets and even most later mass issued rifles with black gunpowder also didn't bring that much of a change to the battlefield. Usual gun range remained similar as fights devolved into chaos from the massed fire. Drills also lacked training on proper marksmanship and the new rifles were actually harder to aim at longer ranges than muskets were. And of course military thinking as you cite was conservative in the effectiveness of rifles and for the reasons I mention prior I would not blame them.

Anyways, I really don't agree with your remark regarding the centuries. You can't really use broad strokes in reference to the 19th century just as you can't really do that for the 20th. There's a huge difference between 1801, 1812, 1830s, 1855, 1865, 1880s and 1890s, for example. Yet these are all the 19th century.[@Romero]'s idea to call this the 19th century is thus neither a misinformer and especially not inaccurate. 1799 has far more to do with the early 19th century than the middle period of the 18th, for example.