So whatever the typical recruit in Europe was (to respect your work on that) in the U.S. most rural boys were familiar with guns, including rifles, and military-grade arms were ordinarily obtainable from the local jewelry or hardware store or via parcel through regular advertisements in big city newspapers. Brisk sellers really (which we know because the ads were repeated).
(...)
Case in point: given the situation, would any of us have casually walked in front the lines 100-200 yards from the enemy, trusting that the boys on the other side were such poor shots. No. Hindsight is cheap.
Except that the number of rifled military grade firearms in the country was limited before the war broke out...
If we followed your reasoning to its full extent, we should expect everyone to be armed with a sharps or Henry... because there where ads for them in newspapers...
That there where ads for them, don't prove that they where produces in huge numbers or that everyone had one... just that a sufficiently number where sold to justify the ads and that there was a limited production happening.
Even if we just want 25% of all recruits to have experience with military-grade rifles, that would still have require more than half a million military grade rifles in the country before 1861... And they where simply not there. Had they been neither side would have resorted to importing old used smoothbores from Europe. (The union alone imported more than one million guns)
If production and availability had been as big as you repeatedly claimed, then the Union would just have produce the guns it needed on its own. But it could not.
As Don Dixon pointed out in another topic:
The Springfield armory managed to make about 6200 "springfields" in 1861.
That is only 17 pr day.
( By the end of 1862 they where up to 280, by end of 1863 they where up to about 600 pr day.)
Since the Federal arsenal could not produce the needed arms, civilian manufacturers was used... but very few guns where delivered until early 1863. Had there been large scale civilian production of comparable military rifled firearms... it would not have taken 1½+ years to get production up at running.
The civilian american arms industry was simply not producing military weapons to that great an extent.
And your 2nd to last point.
The fact that They did "casually walk in front the lines 100-200 yards from the enemy" completely undermine your point.
Either the typical soldier was not a good marksman,
He was not armed with a rifled firearms
Or both.
And both points show that military rifled firearms was in no way common in civilian hands before the civil war.
And the last... Well the romans used Trenches... so I guess they also hard rifled firearms...
Trenched have been around for as long as organized warfare... that they where used during the civil war do not prove anything since they where also used in other 19th century was. Both before and after.