World War 2 was a huge, world wide proving ground for all types of military ammunition.  The worst ammunition made was that of Japan.  The Japanese found that their ammunition was not well suited to the hot, subtropical and tropical environments of the South Pacific.  They had a bad time with dud rounds.  American ammo was better, but it still suffered from duds after total immersion.  In the European Theater of Operations, everyone's ammo worked pretty much as designed. 

 

The sands of North Africa were a different story though.  Everyone had problems with the fine dust getting into everything and jamming actions.  The worst of the jamming problems was faced by the Italians.  For some unknown reason, just about all of their ground machine guns were designed to use lubricated ammunition to keep the rounds from sticking in the chambers.  The machine guns even had a small tank on them so that oil could be squirted on the ammo as it was fed to the gun!  Combine lubricated ammo plus sand and you have a recipe for disaster.  One of the Italian guns used a strip feed (a design feature of the M1914 Hotchkiss machine gun and some Japanese WW2 machine guns) and a very complicated feeding mechanism (along with an oiler).  This machine gun removed the round from the strip, lubricated it, chambered and fired it, and then put the extracted round back into the feed strip; the gun then ejected the strip with 30 fired cases as it started on the next strip.  One thing for certain, Italian units with these machine guns left a tidy battlefield.  The other problem faced by the Italians in North Africa was ammunition related, but also a supply problem: they had just too many different calibers.  Even the standard infantry rifle was going through a modernization when the war started -- calibers were changed from 6.5 Carcano to 7.35 Carcano -- can you imagine the problem getting just the right caliber rifle ammo to units in the field?

 

When NATO was formed in 1949 to act as a military bulwark against expansion of Soviet Russia and its surrogate Warsaw Pact allies into Western Europe, the member nations remembered the problems with their wartime ammunition and, because NATO demanded interoperability and standardization of ammuniition,  NATO standardized ammunition was required to be waterproof.  The Russians and their Combloc allies also realized this and waterproofed their ammunition also. 

 

Waterproofing of ammunition is done as the ammunition is assembled.  A sealant is applied to the outside of the primer cup before it is inserted into the case.  Likewise, a sealant is applied to the bullet just bfore it is seated into the loaded case and seated.  The sealant then cures and prevents the entry of water; it completely waterproofs the round of ammunition.  This ammunition can be totally submerged for long periods of time and still work as it was intended.  For shotguns, the biggest post-WW2 improvement was the change from brass and paper shotgun shells to plastics.  The Plastic rounds are easier to make, cheaper, and do not swell when exposed to water like the cardboard rounds did.  The plastics worked so well that the military retired the all-brass shotgun shells it had been loading for riot and trench guns since WW1 days.  Military shotgun ammunition is waterproofed similarly to other military ammuntion,except for the sealant applied to the crimp that closes the shell.

 

So how do you tell if a cartridge is waterproofed?  Very easily done.  Look at the primer.  If you see a colored ring around the primer where it's seated in the case, that's the sealant.  Look at where the bullet joins the cartridge case.  If you see a colored band around the bullet at the joint, that's the sealant.  This case is totally waterproofed.  Depending on the country of origin, colors of sealant will vary.  Most commercial ammunition is not waterproof nor is ammunition used for match shooting.