Bugfatty300
Buddha Squirrel
Mythbusters showed you could fire guns underwater. When you start talking about clumps of mud and uneven wet spots in the barrel, I don't know what would happen. I wouldn't do it myself, but I believe the story.
I never saw that episode but according to the mythbusters website:
-Tory made sure that there was no air in the barrel because, if there was, the barrel could explode.
-The other guns didn't fare as well. The 12-gauge shotgun cracked on firing with heavy damage to the barrel and stock. The impressive M1 Garand also fared poorly.
http://kwc.org/mythbusters/2006/04/episode_51_myths_reopened.html
In open air with water in the barrel I'd bet you'd get a much different result.