Swaging is the operation of cold forming metal through a die using high pressures. The term swage also can apply to a die used in a swaging operation, or a tool used for swaging.

Swaging in firearms and ammuntion

In Internal ballistics, swaging describes the process of the bullet entering the barrel and being sqeezed to conform to the rifling. Most firearms bullets are made slightly larger than the inside diameter of the barrel, so that they are swaged to engage the rifling and form a tight seal upon firing. Compare to obturate.

In ammunition manufacture, swaged bullets are bullets manufactured by swaging room temperature metals into a die to form it into the shape of a bullet. The other common manufacturing method is casting, which uses molten metals poured into a mold. Since metals tend to expand when heated and contract when cooled, cast bullets must be cast with a mold slightly larger than the desired finish size, so that as the molten metal cools, it will harden at just the right point to shrink to the desired size. In contrast, swaged bullets, since they are formed at the temperature at which they will be used, can be formed in molds of the exact desired size. This means that swaged bullets are generally more precise than cast bullets. The swaging process also leads to fewer imperfections, since voids commonly found in casting would be pressed out in the swaging process.

Individuals who make their own bullets usually cannot afford the expensive hydraulic presses required for swaging bullets, and are thus forced to make cast bullets. To get high precision results, it is common to cast the bullets slightly oversized, then swage the resulting castings through a die to do the final forming. Since the amount of pressure required to size the bullet is far less than that required to form a bullet, a simple mechanical press can be used--often the same press used for reloading ammunition.