You'd be surprised. I've seen old Earth weapons and had to stop and think every now and again. I'm just lucky my hands work well with human-made weapons - some species ain't so lucky.
Leviathans might not, but there's plenty in the galaxy that responds how you'd want to a bullet or rocket being put in them. We'll take stock of what we have and make sure everyone knows what's safe to test and what isn't; safest route.