I wouldn't trust them for other than plinking, but you might set them out and let 'em dry real good and load a few just to see; they might surprise you.
Not quite the same deal, but sometime in the early '90's @ Camp Bullis, I watched a huge black cloud approaching from the north during my prep period on the 800 yd line when the bottom dropped out. Range control had warned of possibility of large hail and thunderstorms just prior to the arrival of a blue norther. Line officer made decision to hold our relay on the line, hoping the cold front would quickly pass and we could continue.
I always put a shelter half down then my mat, leaving half the shelter half out in case of such events and just rolled the tarp over me to keep as dry as possible. The rain did not let up and when it began to hail, I quickly dumped my ammo block into the saddle bags on my stool, gathered up my gear and proceeded to walk back behind the 1000 yard line to wait it out in the shelter of some trees.
When the front did clear, line officer called my relay back to the line. Knowing I could not get there in time, I scratched the 800 & 900 yd relays, but really was wanting to verify my 1000 yard zero, so fell in on the 1000 yd line when my relay was finally called.
When I began to recover my ammo from bottom of saddle bag I was surprised that water was wrist deep in the bag. Apparently I had not secured the flap and the ammo had been completely submerged for probably an hour and a half or more. I do not seal my primers or bullets and was sure the ammo would be compromised, especially since the temperature had dropped probably 20* or more w/frontal passage and would possibly create a vacuum in the cases, but wanted to get rid of those rounds so as not to get any mixed in w/good ammo. Proceeded to shoot all 22 rounds without any noticeable POI change, etc.
Of course those primers were not exposed directly to water, but again, you might be surprised.
Regards,
hm