"Percussion caps came into use before the war. First caps were GD brand costing 10 cents for box of 100. They were unsatisfactory as they wouldn't fire in damp weather."
[From memories of the early life of Franklin Monroe Hudson, born in 1852 in Limestone County, Alabama. Appears that he is telling of events told to him by his father at this point in the narrative.]
I have seen other references that these did not work in the rain.