Definitely a percussion cap as it is now but appears to possibly be a converted flintlock. Let us know what markings you find. Did you measure the caliber? Is the muzzle end bent or did the camera distort the shape? Great find in any event.
HH
dts
It's going into the electrolysis tank tonight. Hopefully that brings out a mark. The end is bent a bit. It looks like it was hit by the plow or run over. I'm not sure of the caliber. I'll have to measure it when I get back from work tomorrow night