Absolutely, Eric,
The oldest datable sources of period artwork depicting powder horns - or, generally speaking, any kind of receptacles for keeping gun powder - are as 'young' as the 1480's (by Diebold Schilling, see my post above).
This is why I set up the thesis that the sidebags worn by everybody up to ca. 1600 served as the first 'receptacles' for powder and ball as well before horns entered the scene:
http://www.vikingsword.com/vb/showth...ht=powder+ball
In the 'Maximilian' period, around 1500, they were called 'pulvertaschen' (powder bags).
Best,
Michael