Time, Ammunition and Oxidation
There was some traffic on various bulletin boards around the 'net a bit ago that indicated some misconceptions about ammunition, airgun pellets, and agespecifically deterioration due to oxidation of the lead.
All metals oxidize. Some metals do this very slowly and others rather quickly, but just as animals age, so do metals. Lead is a very interesting metal in that it not only oxidizes, but it changes its morphology as well with time. Reloaders, particularly those who cast their own bullets, have been aware of this fact for many years: Bullets made on Friday are noticeably softer than they will be on the following Friday! Pellet makers discovered that this tendency of cast lead to vary in hardness and ductility over time as internal crystalline changes took place meant variations in the quality of the pellets they produced. One maker in particular has taken this into account very successfully and now produces pellets of incredible uniformity (compared to 10-15 years ago). The process starts with an alloy formula that resists oxidation to a great degree. Then ingots are poured from this molten mixture. These ingots are then "aged" they sit on a shelf in a controlled environment for several weeks. After this stage, the ingots are put into a machine and drawn into coils of wire. As this mechanical "working" again causes the molecular structure of the lead to start changing, another "aging" period is prescribed and the coils sit on the shelf for more weeks. Finally, the wire is fed into the pellet forming machines and the actual pellet is created. As the mechanical change from wire to pellet is much less extreme than that from ingot to wire, the internal structure of the pellet undergoes far less change and thus remains more stable. The production of each machine is kept separate and about 25,000 to 35,000 pellets are numbered as a single lot. These lots are in turn tested, packed and shipped. The best of these lots (10 shot groups from which must fit inside a 6mm circle) become "World Champion" pellets. While in the past, a shooter had to be concerned that if he or she bought more than 5,000 pellets (one carton), they might not get used up before they "expired" (became oxidized). This has not been a concern for many years. We have pellets in our archives of control samples that are 8 years old and have the same surface appearence as freshly opened tins of pellets a slightly dull silver finish. In the bad old days before the anti-oxidizing alloys, the pellets would first turn a very dark gray-black and then would become covered with a white powder. Lead has several oxidation states, but these are probably all you will see in ammunition and pellets. The dark color is usually of no concern (look at your eley "tenex" or any other .22 bullets they will often be a dark gray). However, the white powder can possibly harm the bore and so ammunition or pellets at this stage of oxidation should be disposed of properly.
Fortunately, science and technology have triumphed again to the benefit of the shooter and this is not a worry with modern factory ammunition and pellets. The reloader, however, might still want to keep a close eye on his efforts!
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