Corbin Rifling Twist Rate Calculator

The Rifling Twist Rate Calculator, also known as the DC-TWIST program, is a specialized software tool that helps you calculate the proper spin rate (rifling twist) for any bullet. Unlike traditional methods, this calculator factors in variables like jacket, core, and tip density, as well as velocity and center of gravity. It even allows for changes in the media through which the bullet travels, such as different air densities or underwater conditions.

DC-TWIST can be run from the USB Flash Drive or installed on your hard drive. Just put the flash drive into a standard USB port, open the folder titled DC-TWIST and run the imbedded application. No technical expertise is required to calculate the proper twist rate for any bullet! At the price, any bullet maker should have this useful tool in their arsenal.

The program adjusts the spin rate required for very low and very high velocities, since the rate of spin generates different centrifugal forces on the bullet as the velocity changes. Once the bullet is free of the barrel, the velocity has little effect on required spin, but since velocity determines the bullet rotational speed imparted by the rifling twist, a higher twist rate would be required to stabilize a bullet fired at very low speed compared to firing the same bullet at a high speed. This is a neglected factor in conventional Greenhill calculations. Obviously, at zero forward velocity there is no rotation imparted, and at very low forward velocity, the same numbers of turns per unit of distance generates a very small number of revolutions per minute, but the usual method of calculating stable twist has no input factor for varying velocity.

Likewise, a bullet with the center of gravity (CG) shifted far to the rear will require much higher spin rate to maintain nose-forward attitude compared to a bullet with the CG shifted further forward. Most bullets have their CG somewhat to the rear of the linear midpoint. If dropped from a height with the nose pointed down, they would land base first. A nose-heavy bullet, on the other hand, would land nose first. In flight it would require less spin to maintain nose-forward attitude.

With the CG moved too far forward, the bullet would require little or no spin to strike nose first, but would follow the launch angle of attach over its trajectory path. Said differently, the nose would continue to point in the direction and angle at which it left the barrel, so that as the trajectory arc became larger with greater distances, the bullet would tend to fly at an angle to the direction its nose pointed, and would induce tumbling. 

DC-TWIST considers the location of the bullet CG, so that with all other parameters equal, a bullet with the weight shifted forward, such as a hollow base wadcutter, an airgun pellet, or a hollow base shotgun slug, would require less spin than a bullet having a long pointed nose and a flat solid base. Likewise, bullets composed of different density materials, such as tungsten powder base sections and plastic nose fillers, would require different spin rates than the same weight and size of bullet with the same average density in a monolythic core design.

The program allows for location of the CG relative to the center of form, as a percentage from the base to the tip. Entering a value more than zero and less than 100 lets the design engineer shift the balance of the bullet and determine the effect on stable spin rate. 

• Main Purpose: Calculates the proper spin rate (rifling twist) for any bullet
• Compatibility: Can be run from Flash Drive or installed on your hard drive
• Features: Factors in jacket, core, and tip density, as well as velocity and center of gravity
• Additional Info: Allows for calculations in both English and Metric units, and can save and print data

Benefits

• Precision: Provides highly accurate calculations for rifling twist rates, improving bullet performance.
• Versatility: Allows for calculations under varying conditions, including different air densities and media.
• Ease of Use: User-friendly interface with options to save and print data, making it convenient for repeated use.

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