On a long table under a tent, Day showed park visitors several types of rifles that were produced in Harpers Ferry and other weapons that influenced weapon-making in the small river town.
One of those was a flintlock rifle produced by John Harris Hall.
The Hall Breech Loader - introduced in 1819 - was significant because unlike other rifles, it began the use of interchangeable parts, which made gun repair simpler, said Day.
Hall's gun "created a wave" in Harpers Ferry because it meant that machinists, rather than artisans, would be needed to manufacture such a rifle, Day said.
The Hall Breech Loader led to the development and manufacture of the Model 41 rifle in Harpers Ferry in 1846, she said.
"This is kind of a good introduction of what first came out of our factory," said Day, referring to the rifles in front of her.
At one time, about 10,000 guns a year were manufactured in Harpers Ferry, the industry took up about 20 buildings in town, and it employed about 400 people, park officials said.
Harpers Ferry's gun-making operations made the town a prime target at the beginning of the Civil War, which was illustrated by abolitionist John Brown's attempt to take over the armory as part of his plan to set up a free state for blacks, Day said.
Some of the guns exhibited Sunday were reproductions of the ones made in Harpers Ferry. Some original Harpers Ferry guns can still be found and as many as 100 can be seen at large gun shows, said James Cross, a member of the Youth Conservation Corps that was helping lead another gun exhibit in the park.
Groups of tourists filtered into the park to see the exhibit and enjoy sunny, summer-like weather.
Brent Cummins and Amy Haugh of York, Pa., said Sunday marked their first visit to the park. They decided to visit after camping on some nearby land that they come to frequently.
"It's very educational, interesting," Cummins said.