2, the die extrusion method is also called the overhead method. Rifling method was invented by mike walker, an engineer of Remington Company in the United States, in the 1950' s. The method is to drill a small hole at one end of the barrel, and then use a high-hardness die with a protrusion corresponding to the mother rifling to press the material from the hole with a high-pressure machine to form mother rifling and rifling.
3. Extrusion and cutting are "rifling", but the tools used are different. Cutting will lead to sharp rifling, but the manufacturing speed is fast; Extrusion will be slower, but the rifling is smoother, which is very suitable for small caliber guns, especially short barrel rifling. The technical term is "button rifling", but the word "cutting" is also used in many cases.