Here's a look at the concept of rifling and how it relates to bullet stability. The earliest firearms had simple tubular bores, like a modern shotgun.
In the late s, gunsmiths in what is now Germany developed a method of scraping grooves in barrels to allow room for blackpowder and lead fouling to build up, hopefully prolonging the accuracy of the barrels before they needed to be cleaned. They found, eventually, that by twisting these grooves in a barrel, they could dramatically improve its accuracy. Rifling works by spinning the projectile about its axis, causing gyroscopic forces that spin-stabilize it throughout its flight; tighter rifling will spin a bullet faster, while looser rifling will spin a bullet slower.
The rate at which the bullet is spun is very closely tied to how stable it will be; too slow, and the bullet will tumble in the air, too fast and the bullet may break apart in flight.
An M4 Carbine with a fairly new barrel firing 5. The Firearm Blog is a news site dedicated to all things firearms related. TFB covers top stories in the firearms industry. TFB staff writers share a passion for firearms but come from a diverse background, stretching from the world of law enforcement to being deployed on the streets of Fallujah, Iraq to the woods hunting wild game.
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Download a brochure now! Streamlight From Southern Police Equipment. A65 From Southern Police Equipment. Button rifling is also a highly controlled process that is repeatable across an entire production lot. Progressive twist is possible with the button rifling process. Cons of Button Rifling - With button rifling, an additional stress relieve step is required adding cost and time - the stress relieving operation is used to relieve stress introduced in the bore of the barrel because of the cold forming process.
Also, pre-machining of pistol barrel features is not possible, as a uniform outside diameter is necessary due to the swaging performed when button rifling. A unique tool is needed for every twist, as the helix is ground into the carbide button. Manufacturability - Button rifing is easily done on modern equipment. Servo control of the twist rate, compared to older sinebar or cam technology, has greatly improved the uniformity of twist throughout the barrel, as well as enabled repeatability throughout a production lot.
Availability and relatively lower investment of equipment also makes button rifling an advantageous method. Popularity - Because of the simplicity, consistency, and short cycle time that button rifling offers, this is by far the most commonly used process in rifle barrel manufacturing by volume.
Typical Applications - Hunting rifles, MSR style rifles as well as some precision rifles and some pistols. Video Reference - View the button rifling process. Also referred to as Hook Rifling, this is a metal cutting process that uses a carbide "hook" to cut a single groove in the barrel.
The process requires several passes to cut the groove to its final depth. The tool cuts one of the grooves, indexes, then cuts the next groove and indexes again until the desired number of grooves have been cut.
The hook is advanced out or deeper via a wedge type system, and the process is repeated. The whole cycle may include many passes to achieve the final depth of the groove in a barrel. Pros of Cut Rifling - The metal cutting process does not introduce additional stresses in the metal, as compared to a cold forming processes, so the barrel does not require post stress relieving. Manufacturers have great control over groove depth due to the minimal depth of cut per pass and the number of passes per cycle.
By simply running another pass, the groove can be cut slightly deeper to achieve the desired groove diameter. Because the tools are not specific to a twist rate, manufacturers are able to use a single tool for a range of rifling configurations. Advancements in modern machine design and the use of servo technology allows operators to easily program a gain twist with the same tool, while modern CNC technology enables a simpler, more repeatable operation.
Cons of Cut Rifling - Cut rifling is a very time consuming process due to the number of cuts and minimal amount of material removed per cut.
It does require a skilled tradesman to operate the machine and process parameters as compared to other rifling methods, where variables are highly controlled by the machine. Repeatability is hardest to maintain with cut rifling.
Bore diameter uniformity before the cut rifling process is very important as the cut rifling tool body locates on the bore while cutting the groove. Manufacturability - A purpose built machine with custom tooling is required and is often custom built by the barrel manufacturer.
With cut rifling, repeatability and stiffness of the rotation relative to linear motion is critical and difficult to achieve both in machine design and manufacturing process. Manufacturing Cost - Tooling - medium; Machine - medium; Cycle time - high. Popularity - Cut rifling is still a common manufacturing process, but cut rifled barrels only make up a small percentage of barrels on the market.
Broach rifling is a metal cutting process that uses a long tool with multiple teeth that take small amounts of material out of each groove. The broach is fed down the barrel with a rotation that matches the twist ground in the tool, with each progressive tooth increasing the depth of cut. This is a similar process to single point cut rifling, but only requires a single pass. It can be done on a similar machine to that of button rifling. Pros of Broach Rifling - Simiar to cut rifling, additional stress is not introduced into the material.
However, broach rifling does offer a distinct cycle-time advantage, which is more comparable to that offered by button rifling, by using a single pass. Cons of Broach Rifling - With broach rifling, a tool is needed for every twist rate, and the tool design prohibits progressive twist. Chip control is an important consideration for manufacturers. Finally, surface finish is not as smooth as that resulting from other rifling processes.
Tooling costs can be very high, and the tools are relatively fragile, potentially adding even more costs or interrupting production.
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