I dont know for sure at what point guys waterproof their ammo, what I do know is that on a very wet hunt last year the bag I had my ammo in filled with water accidently and for several days. I later took that same ammo to the range and fired them at 300 yards. They all hit their mark and grouped well. I do not know however if that would happen every time. I imagine that it would depend on how tight tolerances are ect..
So in other words it really isn't worth it. My only reason for asking the question was incase you or your weapon were stuck in the rain for extended periods without worrying if your ammo would still work.
Johnson's floor wax, paste style, works fine for this scenario.
Make sure your cartridges are clean of any finger oil. Apply the wax at the case mouth/neck joint and around the primer. Force it into the crevice just as you would when waterproofing the welts of your hunting boots. Easier if you warm the wax a bit. Clean off the excess and you're ready to go.
Some plastic ammo boxes have a collet style insert that the bullet and neck go into and these can scrape the wax protection away. Best packed bullet up in this kind of carrier.
I use my wife's fingernail polish on the primers for my hunting rounds. Take a toothpick and a couple paper towels. Get a small drop on the toothpick and guide it around the edge of the primer. After doing this, I push and twist the primer into a paper towel while hoplding the case a sflat as possible. this removes any excess polish and fills the edges nicely.
I should have been more specific in my post regarding wax application.
Regarding the primer, excess wax should be removed with a cotton swab. Using a rag leaves too much wax which will be deposited upon the bolt face after firing. Use the cotton swab in a perpendicular orientation to wipe the primer pocket perimiter. This will leave plenty of wax down in the crevice to achieve water tightness.
Regarding the case mouth/bullet seal, the excess wax should be wiped off with a tight rag held between thumb and forefinger while the other hand rotates the cartridge. This will remove nearly all the visible wax leaving only a miniscule seam similar in design to the grouting or caulking seal found around bathtubs and such.
The wax at the case mouth does indeed fire off when the cartrdge is discharged. I've found no evidence of wax collection in the chamber as a result of using rounds so addressed and I've been doing this on my 375 H&H ammunition for over thirty years now. (factory chamber and barrel)
I prefer not to use paint products on my ammo as they all have powerful solvents and the resultant vapour trails inherent in such products. The possibility of violation, while remote, has always nagged me. The wax works and has been completely free of contraindications in my experience.
I have never waterproofed my tactical ammunition as I am an avocational operator these days and seldom drag my gear out in unfavourable conditions.
When hunting elk and other big game with my old 375, I generally carry watertight ammo as I operate solo and without benefit of modern field quarters. How does one experience the primal drive of the hunt when encumbered with noisy machines and RVs with hallucinogenic colour schemes?