George Washington's Lost Camp
Just a point to bring up here, on the subject of the musket balls: The standard British Army long arm was the .75 caliber muskets, aka the Brown Bess or Land Pattern Musket, from 1722 until well after 1841 when it's replacement was introduced. So the fact that these guys found a bunch of .69 caliber rounds is far from proof that they found a Royal Army camp; actually it tends to disprove it.
The French Army at the time was using the Charleville Musket (.69 caliber). So finding a collection of those rounds would indicate one of their camps, not a British one. I was quite surprised that the "experts" hired to analyze the artifacts did not know that.
Once the American Army was established as a regular army and a government armory (Springfield, Massachusetts) was built the Model 1795 Musket began production but it also was .69 caliber, emulating the standard French weapon.