- Barrel Twist
- The twist rate (inches per turn) of the barrel. This value is used
to calculate stability. It should not be confused with the required twist
calculated by Bullet Drag.
- Base Diameter
- The diameter of the base of the bullet. For boattails, this is
smaller than the caliber.
- Boattail Length
- The length of the boattail from the rear of the bearing surface to
the base of the bullet. It is zero for flat base bullets.
- Bullet Specific Gravity
- The density of the bullet, relative to the density of water (1.0).
10.7 is a commonly used value for jacketed bullets.
- Bullet Weight
- The weight of the bullet.
- Diameter of the bullet's bearing surface (that part that contacts
the rifling of the barrel), measured in inches.
- Drag Function
- The drag function to use to calculate the ballistic coefficients.
Most commercial bullets use the G1, but for some long range bullets, the G7
or G8 is typically a better choice. Some military bullets fit the G5 and
G6 functions better than the G1. The GL is for high drag bullets and won't
really fit anything that Bullet Drag can calculate coefficients for. GI is
the Ingall's drag function and is thrown in for fun.
- Meplat Diameter
- The diameter of the flat portion of the tip of the nose of the bullet.
For some bullets, the meplat diameter is zero (or very close).
- Muzzle Velocity Units
- Units used to calculate muzzle velocity on output.
- Nose Length
- The length of the nose from the front of the bearing surface to the
- Nose Type
- One of Secant, Tangent or Conical. A secant nose is one in which the
center of the circle describing the ogive is located behind (away from
the nose) the point of intersection of the ogive and the body of the bullet.
A tangent ogive is tangent to body at the point of intersection of the
ogive and body of the bullet. A conical nose shaped like a cone. It's
radius is effectively infinite.
- Ogive Radius
- The radius of the nose ogive. For conical bullets, this value is
not used since the ogive radius is essentially infinite.
- Rotating Band Diameter
- The diameter of the rotating band, if any. Most small arms bullets
do not have rotating bands (although the rear of the bearing surface may
be 1/10000's larger than the caliber, Bullet Drag Calculations do consider
this a rotating band) and therefore the rotating band diameter is equal to
- Total Length
- The total length of the bullet from the base to the meplat.
- Ballistic Coefficient
- The ballistic coefficient calculated using the drag function you
- CD Boattail
- Boattail drag coefficient.
- CD Base
- Base drag coefficient.
- CD Nose
- Nose drag coefficient.
- CD Rotating Band
- Drag coefficient due to the rotating band, if any.
- CD Skin
- Component of the drag coefficient due to the skin drag.
- CD Total
- The bullet's drag coefficient. It is the sum of the components of
the drag coefficient above.
- Form Factor
- The form factor for the bullet. This is a ratio of the actual CD
of the bullet to that of the CD of the "standard" bullet for the selected
- Mach Number
- Mach number for the given velocity and atmospheric conditions.
- Muzzle Velocity
- Calculated muzzle velocity for the mach number at standard conditions.
- Stability factor for the bullet at the given muzzle velocity. It
should be greater than 1.5 to ensure stability. These stability factors
are calculated with the twist you entered since the required twist would
always give 1.5! The background will be green when the bullet is stable
and red when it is not.
- Sectional Density
- Bullet sectional density
- The required twist to achieve a stability of 1.5. The background will be
green when the bullet is stable and red when it is not.