On the previous page we populated the Gun Tube Definition tab using data from the reference book. If you are dealing with a new weapon, there is a bit more work to do. First the parameters on the left need to be entered. Most are self self explanatory or were discussed on the previous page, but a couple warrant additional clarification.

• Barrel Length is the travel of the projectile in the gun tube. We generally measure from the forward edge of the rotating band to the muzzle of the gun barrel.
• Projectile Free Travel is the distance from the forward edge of the rotating band to the initiation of rifling in the barrel. If Free Travel is "zero" then it is assumed that the rotating band is seated in the rifling and that rotation will occur with no slip as soon as motion begins. If Free Travel is positive, then rotation starts when the forward edge of the band reaches the initiation of rifling. Full rotation (zero slip) will not be achieved in this case until the aft edge of the band reaches the initiation of rifling.

Next the rifling profile table must be defined. This table is pairs of points defining the rifling twist (or helix angle) at various points along the length of the barrel. There are a couple of rules that must be followed when defining this table.

1. The first point must have a "0" axial location. This point corresponds to the initiation of rifling in the barrel. The twist at this first point may be "0" or any positive value.
2. Axial Location and Twist must be positive values.
3. Axial Location must increase with each row in the table.
4. The last row in the table must have an Axial Location greater than the Barrel Length.

A constant twist barrel may be defined using only two point, both with the same value of twist as shown in the example below. Note that the first point is at "0" Axial Location and the last is well beyound the end of the barrel.

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