From Spud Wiki
In order to more accurately send a vegetable projectile towards the desired target, barrels for produce accelerators can be "rifled" which produces spiral grooves on the inside surface of the barrel.
These grooves impart rotation to the projectile as it accelerates down the barrel, gyroscopically stabilizing it and preventing the projectile from tumbling end-over-end. This spinning motion has been demonstrated to have positive effects accuracy of potatoes, as seen in this test done by Burnt Latke.
The rate of twist required can be approximated through a version of the Greenhill equation that has been modified to take into account the density of the projectile, though one must remember that the Greenhill equation was developed to deal with supersonic, pointed, and very dense projectiles: Twist = (C*D2)/L * sqrt(SG/10.9)
- Twist = number of inches per rotation
- C = 150 (use 180 for muzzle velocities higher than 2,800 f/s)
- D = bullet's diameter in inches
- L = bullet's length in inches
- SG = bullet's specific gravity
Rates of twist higher than this should not hurt accuracy much, unless they break off the bits of potato that are engaging the rifling and thusly transmit no rotation at all.
Rifled barrels were formally available from SGTC prior to it's closing.
See also spudgun accuracy