And by and large, participants take pride in being as accurate as possible.
Food is often cooked over open wood-burning flame while soldiers rest after battles; all reenactors try to keep everything from their socks to their glasses period accurate; and many sleep on the ground with their heads poking out from their tents.
But some details within camps can also be less than historically accurate, which irks some of the more particular participants.
"That is obscene to us," declared Greg Moore, from Portland, Ore., pointing toward the rows of cars that could be seen from the Union camp.
Moore, who says is discerning when it comes to maintaining period accuracy, described other scold-worthy offenses, such as men drinking Gatorade from tin cups, hoop-skirted women exiting porta-potties (a luxury that didn't exist in 1863), and soldiers sitting in tents texting loved ones.
While sitting with a group of friends from the First Oregon Volunteer Infantry - one of whom had a lunch sandwich containing cold cuts - Moore said that reenactors display a variety of authenticity levels.
But there's a relatively universal word to describe anyone using anything modern, he said: a farb.
The word, reenactors say, is shorthand for a phrase that they use to heckle period-accuracy violators. If a participant is caught on a cellphone, for example, a reenactor would bellow, "Far be it from me to say they didn't have those in my day."
Erek Dorman, 45, from Strasburg, Va., said that "farbs" are just one level on the period-authenticity pyramid: the most accurate are "campaigners," who journey to the battle with the sparsest supplies; "mainstreamers," he said, are generally concerned with simply enjoying themselves.
Dorman, a Union colonel and senior military aide to the Union commander, said he has been texting his wife on occasion this week, and that this, for most reenactors, is a tolerated modern amenity.
Another was the Union command using blowups of Google Maps screen shots to ensure that the battles are planned safely.
"We try and be tactful about it," he said of reminding reenactors to be period-accurate.
And while many non-reenactors would wonder why anyone would eschew phones, showers, or mattresses for a few days, that's simply an essential part of what reenactors call "the hobby."
For Adam Bell, 29, of East Palestine, Ohio, it's what sets the hobby apart.
"If you're going to differentiate between this and playing 'war' when you're a kid," he said, "you have to do the stuff that's not enjoyable."
Contact Chris Palmer at 609-217-8305, firstname.lastname@example.org, or follow on Twitter @cs_palmer.