Editing Rifling (section)

== Manufacture ==
[[file:Aciéries de Saint-Chamond - Rayage des canons de 75 - Saint-Chamond - Médiathèque de l'architecture et du patrimoine - APZ0001439.jpg|thumb|Rifling a [[Canon de 75 modèle 1897|75-mm gun]] barrel during WWI]]
{{Further|Internal ballistics}}

An early method of introducing rifling to a pre-drilled barrel was to use a cutter mounted on a square-section rod, accurately twisted into a spiral of the desired pitch, mounted in two fixed square-section holes. As the cutter was advanced through the barrel it twisted at a uniform rate governed by the pitch. The first cut was shallow. The cutter points were gradually expanded as repeated cuts were made. The blades were in slots in a wooden [[dowel]] which were gradually packed out with slips of paper until the required depth was obtained. The process was finished off by casting a [[Slug (projectile)|slug]] of molten lead into the barrel, withdrawing it and using it with a paste of [[Emery (rock)|emery]] and oil to smooth the bore.<ref>{{cite book|last1=Wilkinson|first1=Henry|title=Engines of War, Or, Historical and Experimental Observations on Ancient and Modern Warlike Machines and Implements|date=1840|publisher=Longman|location=London|pages=108–110|oclc=254626119}}</ref>

Most rifling is created by either:

* Cutting one groove at a time with a [[machine tool|tool]] (''cut rifling'' or ''single point cut rifling'');
* Cutting all grooves in one pass with a special progressive [[broach (metalwork)|broaching]] bit (''broached rifling'');
* [[Machine press|Pressing]] all grooves at once with a tool called a "button" that is pushed or pulled down the barrel (''button rifling'');
* [[Forge|Forging]] the [[gun barrel|barrel]] over a [[mandrel]] containing a reverse image of the rifling, and often the chamber as well (''hammer forging'');
* [[Shear forming#Flow forming|Flow forming]] the [[gun barrel|barrel]] preform over a [[mandrel]] containing a reverse image of the rifling (''rifling by flow forming'')
* Using non-contact forces such as [[chemical reaction]] or [[heat]] from [[laser]] source to [[Etching|etch]] the rifling pattern (''etching rifling'')
* Machining the rifling grooves texture on a thin metal plate, then folding the plate into the inner bore of the barrel (''liner rifling'')

The ''grooves'' are the spaces that are cut out, and the resulting ridges are called ''lands''. These lands and grooves can vary in number, depth, shape, direction of twist (right or left), and twist rate. The spin imparted by rifling significantly improves the stability of the projectile, improving both range and accuracy. Typically rifling is a constant rate down the barrel, usually measured by the length of travel required to produce a single turn. Occasionally firearms are encountered with a ''gain twist'', where the rate of spin increases from chamber to muzzle. While intentional gain twists are rare, due to manufacturing variance, a slight gain twist is in fact fairly common. Since a reduction in twist rate is very detrimental to accuracy, [[gunsmith]]s who are [[machining]] a new barrel from a rifled blank will often measure the twist carefully so they may put the faster rate, no matter how minute the difference is, at the muzzle end.