I got burned in such a way. I was wearing shorts at the time. I got boiling water on my thigh and knee. I got no burns on my naked knee, first degree burns on most of my thigh, and second degree burns under the cellphone in my pocket where water pooled.
You can't avoid the burn, but you can...
Grapeshot was actually a prepared ammunition; musket balls packed into tin cans. They never jammed nails willy-nilly into a cannon; it wouldn't be that effective.