Surplus ammunition is extra ammo that has become available to parties beyond the original contract recipient - often a government. Sometimes the ammo has become obsolete due to age, weapons systems changes or a variety of other reasons. When this happens, governments are able to recoup a portion of their expense by selling this ammo as surplus. In the past, military surplus ammo from the U.S. was often sold to the public, but the military has lately needed more and more ammunition, reducing the available ammo and drying up the surplus market. The U.S military is not the only source of surplus ammo. Russia and Germany as well as many former Warsaw Pact countries sold and still sell massive volumes of military surplus ammunition.
The surplus ammo buyer, whether the ammo is being resold by a government due to changing weapons systems, or because too much was made, can be confident that the ammo is high quality ammo and was manufactured to strict standards. The only real concern when it comes to surplus ammunition is that some primers when fired will deposit a residue in the bore of potassium chloride salt, which is a corrosive compound that can eventually damage the barrel if it gets left in a weapon for long time without being cleaned out. Most ammunition that utilized this compound was manufactured more than fifty years ago, however, it is possible to find some surplus ammunition with this compound produced into the 1980’s.
It is still easy to find ammunition made in the 1940’s and 50’s, .30 carbine and .45 ACP being the calibers with the greatest available volume from this era. Other surplus ammo calibers available in abundance are .30-06, 8mm Mauser and 7.62x54R as governments purge their ammunition storage facilities to create space for the ammunition used in newer firearms. 7.62x39mm and 5.56mm are not quite as common, but can be found occasionally.
Military ammo can be subject to rough handling and the full spectrum of environmental conditions, so much surplus ammo can be bought in metal cans for storing long term. Shooters find this a great added value if they wish to stock up on ammunition, or if their firearm is chambered in a rare or obsolete caliber. It is important to remember when buying military surplus ammo, that it is dangerous to fire 5.56mm ammo in rifles chambered for .223. The pressures will be too high and there is severe risk of injury and damage to the firearm. 7.62mm NATO and .308 Winchester, while similar, also have different case dimensions which result in increased pressures too. Know which cartridges your firearm can and cannot shoot, and don't take risks just to save a few bucks.
Collectors of military paraphernalia place great value on ammunition boxes and accessories. They display the cans personally and in museums. Shooters of surplus ammunition often find that surplus ammo shoots just as well as commercial ammo, or sometimes even better. The only real downside to surplus ammo is that most surplus ammo cannot easily be reloaded since the cases use Berdan primers which makes reloading more difficult.
Surplus ammo is a great value for the money, and can allow many fine old firearms to keep shooting for years to come.