Barrel swaging is a process used to form barrels by hammer action (manual / pneumatic / hydraulic).

Metal is hammer forged around a mandrel. It forms the shape of the bore and the basic contour.

aka:

• hammered barrel
• hammered rifling
• hammer forged

Footnotes / Sources:

“Glossary ⇒.” Sporting Arms and Ammunition Manufacturers’ Institute. Ed. SAAMI’s Technical Committee. Web. 15-18 Jan. 2011.