I had a good deal of ammo exposed to fire hose water and steam when my house burned.
None, nada, zero of the jacketed bullet ammo is good enough for even slow fire plinking. Specifically including S&B with red lacquer at primer and bullet.
A majority of the lead bullet reloads are usable for practice, some lots with an occasional misfire but many fewer than jacketed factory or reload, some lots with no misfires yet.
This indicates to me that the main entry for water was around the bullet and the oversize lubed or coated lead is a better seal than a smooth jacket, even with a dab of Czech red.
I have found a good deal of soggy powder when pulling down ammo to salvage bullets and brass. More dry, though; not all or even most were penetrated. I have shot some of the apparently dry powder and it shoots ok. I have air dried some primers to try.
I don't know how my experience applies to cold water immersion in a kayak, but I would be doing some testing of sealants.