Bullet casting

A cast bullet is made by allowing molten metal to solidify in a mold. Most cast bullets are made of lead alloyed with tin and antimony; but zinc alloys have been used when lead is scarce, and may be used again in response to concerns about lead toxicity. Most commercial bullet manufacturers use swaging in preference to casting, but bullet casting remains popular with handloaders.

Firearms projectiles were being cast in the 14th century. Iron was used for cannon, while lead was the preferred material for small arms. Lead was more expensive than iron, but it was softer and less damaging to the relatively weak iron barrels of early muskets. Lead could be cast in a ladle over a wood fire used for cooking or home heating, while casting iron required higher temperatures. Greater density of lead allowed lead bullets to retain velocity and energy better than iron bullets of the same weight and initial firing velocity.

Swaging, rather than casting, became a preferred manufacturing technique during the 19th century industrial revolution; but cast bullets remained popular in early rimmed black powder cartridges like the .32-20 Winchester, .32-40 Ballard, .38-40 Winchester, .38-55 Winchester, .44-40 Winchester, .45 Colt, and .45-70. Disadvantages became evident as loadings shifted to smokeless powder in the late 19th century. Higher velocity smokeless powder loadings caused lead to melt and be torn from soft bullets to remain in the barrel after firing in small deposits called leading.. Manufacturers of high-velocity military ammunition modified their bullet swaging process to apply a thin sheet of stronger metal over the soft lead bullet. Although it took several decades to devise bullet jacket alloys and manufacturing procedures to duplicate the accuracy of cast bullets at lower velocities; jacketed bullets were more accurate at the velocity of 20th century military rifle cartridges. Jacketed bullets also functioned more reliably and are less likely to be deformed in the mechanical loading process of self-loading pistols and machine-guns.

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