You might try the NPS at Harpers Ferry, on the confluence of the
Shenandoah and Potomac rivers, once in three states, Maryland,
Virginia and West Virginia. Many industrial sites were there, however
the Harpers Ferry Rifle factory was quite large and right in the town.
In 1978, there was a small exposed excavation unit, right in the
"downtown" where many floods have come and gone, where George
Washington wanted to built a large power dam. In the "pit" were the
remains of twisted guns and their barrels where the Harpers Ferry
Armory had burned down in the American Civil War, the unit also near
the since moved firehouse where John Browns Raid was fought out with
Federal troops before Robert E. Lee, former Commandant of the West
Point Military Academy (an artillery student fired the "first shot" at
Fort Sumter, where his former West Point teacher commanded, they known
to argue. I worked in the West Point Foundry Site across the Hudson
River from the Academy).

The interpreter had a number of rifles, and recreated, by active
firing of them, the history of the "firestick" by demonstration, I
think rain or shine, it was a sunny day, I have similarly heard a
cannon fired at Antietam, one of the bloodiest battles in the US Civil
War and have been to Shiloh, TN, where three Parrott cannons (forges
at West Point Foundry) are stood on end and crossed in a tripod, their
muzzles buried in the ground, while working on the Tenn-Tombigbee
Canal, connecting the Tennessee River with Mobile, Alabama.

Very few examples of the Harper Ferry Rifle exist, a percussion cap
gun if I recall, though the gunsmith's instruments survive, and were
on exhibit. A Sunday examination of a few antique shops in the
vicinity only turned up one, that in disrepair, and repaired.

There is also an NPS firearms collection at one of the Civil War era
"bombproofs" at Fort McHenry National Monument in Baltimore, MD, the
Bowie collection, which contains many rifles. I am not sure however
that would actually help, but someone there might be able to give
better advice than this tour of the "bellum".

George Myers