Shotshells will surprise folks as to how
Water Resistant they are.
The term
Waterproof constitutes a different connotation. FTC for instance forbids a Watch to markded "proof" - a watch Mfg can tell how you how "resistant" and to what depth. ( 50, 100, 300, 600..marked either in ft or m- depends)
That said - Yes we used to leave shotshells in the Duck Blinds for the whole season, exposed to cold, wet freezing weather - they always went bang, even the ones we had to break the ice to get into the Coffee can we kept them in.
Along came steel shot..these rust, will ruin a bbl and/ or choke with that glob or rusty metal exiting a bbl.
Candlewax, is great for the holes in shells that don't get a good crimp, or the hull has been reloaded to much.
Slugs are sealed pretty well too, now I have sealed the slugs with Candlewax as well - inclement weather. Even rolling around in the bed of a truck all season long, they fired.
Slugs- RIG Grease, Lithium, and even Chapstick I have used , when using a canoe or flatbottom to get to where I wanted to hunt. Chapstick makes a great line dressing for fly lines too.
I miss the offerings in paper hulled loads tho'