Out of curiosity I have soaked two caps with water.
They did not explode on contact with water - good! (some pyrotechnic materials react strongly with water).
Mass inside cap became a paste that could be moved around and shaped.
After about 12 hours (maybe faster, I only checked after this time) it got dry and hard again.
Surprisingly (?) caps worked correctly, with a big satisfying bang.
Note: do NOT attempt playing with caps unless you use eye protection and other applicable safety measures.
Remember, cap has enough force to blow back metal bolts and slides!