MPM Terms

Input Data

Altitude
Used in estimating the atmospheric conditions. This value is not used unless the Standard Conditions at Altitude checkbox is checked.
Axial Moment of Inertia
The moment of inertia about the centerline axis of the bullet.
Azimuth
The horizontal (side to side) angle the barrel makes with the line of sight. This value is not generally known and can be ignored if the "Azimuth Correction for zero range" option is checked.
Azimuth Correction
If checked, the azimuth is changed to make the bullet cross the line of sight at the zero range -- zero windage at the zero range.
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.
Boundary Layer
The flow over the bullet at the boundary layer. It can be entirely laminar (laminar-laminar), laminar then turbulent (laminar-turbulent) or completely turbulent (turbulent-turbulent). McCoy states that this should be laminar-turbulent unless you know better (e.g. have pictures of the flow).
Bullet Weight
The weight of the bullet.
Caliber
Diameter of the bullet's bearing surface (that part that contacts the rifling of the barrel), measured in inches.
Cant Angle
The angle of the tilt of the firearm to the right or left from vertical. Positive angles are to the right.
Center of Gravity
Distance to center of gravity from nose in calibers.
Chronograph Distance
The distance from the muzzle of the firearm to the chronograph used for muzzle velocity measurements. If the muzzle velocity is estimated, enter 0.0 for this value -- no correction.
Drop Units 1st Column
A drop value (the number you enter) and its associated units. Output windage for the first column are multiples of this value/units combination. See the drop units topic for more information.
Drop Units 2nd Column
Same as Drop Units 1st but for the second column of drop, windage and lead.
Core Depth
Distance from the tip of the bullet to the top of the lead (or other material) core.
Core Specific Gravity
Specific gravity of the bullet core
Direction
Firing direction in degrees. This is the compass direction the firearm is pointing. North is 0° East is 90°, South 180° and West is 270°.
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. This value is only used for calculating the ballistic coefficient.
Elevation
The vertical angle the barrel makes with the line of sight. This value is not generally known and can be ignored if the "Elevation Correction for zero range" option is checked.
Elevation Correction
Or Drop correction, causes the elevation to be raised as required to cause the bullet to cross the line of sight at the zero range. Without this box checked, the zero range is ignored.
Include Aerodynamic Jump
If checked, the effects of aerodynamic jump (wind at the muzzle) are included in the trajectory calculation
Include Coefficients
If checked, the ballistic coefficients used to calculate the trajectory are included in the output
Include Coriolis Effects
If checked, the coriolis effects are included in the trajectory calculation
Include Magnus Effects
If checked, the magnus effects are included in the trajectory calculation
Jacket Length
This value is the length of the jacketed portion of the bullet. This will typically be equal to the length of the bullet, but for those bullets with a lead tip, this value will be less than the total length. NOTE: if you have a jacket length less than the total length, the program sets the core depth to zero.
Jacket Specific Gravity
Specific gravity of the bullet jacket.
Jacket Thickness
The thickness of the jacket.
Line of Sight Angle
The angle between the line of sight and level ground. This value is used when shooting uphill or downhill. Value is a positive angle when shooting uphill and a negative angle when shooting downhill.
Maximum Range
The maximum displayed range.
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).
Minimum Range
The minimum displayed range. Data is calculated from the muzzle the maximum range, but may be displayed from the minimum to the maximum range. (e.g. with a minimum of 990, maximum range of 1010 and a range increment of 10 you would see data 990, 1000, 1010 yards).
Muzzle Velocity
The velocity of the bullet as either (1) measured at some distance from the muzzle or (2) as estimated from reloading data. The on-line ballistics page can correct for the distance to chronograph. (The velocity lost traveling to the chronograph.)
Nose Length
The length of the nose from the front of the bearing surface to the tip.
Ogive Radius
The radius of the nose ogive. For conical bullets, this value is not used since the ogive radius is essentially infinite.
Point Mass Trajectory
This option forces the calculation to use only the drag term dropping other effects like aerodynamic jump, drift and magnus. The spin rate and coriolis effects (if checked) are still calculated.
Pressure
The barometric pressure. It must be an absolute pressure, not a corrected station pressure.
Range Increment
the increment used in displaying the calculated data.
Ranges in Meters
When checked, all ranges entered (minimum, maximum, increment and zero) are in meters.
Relative Humidity
Relative humidity (percent)
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 the caliber.
Sight Height
The height of the sight (or scope) above or below from the centerline of the barrel. This is required because the bullet starts at a drop of -[Sight Height].
Sight Offset
The offset of the sight (or scope) to the left or right of the centerline of the barrel.
SPINNER CLα, CMα and CLp
This program has two methods for calculating CLα, CMα and CLp, GE's SPINNER program or Bob McCoy's INTLIFT and McDrag program. If checked (default), SPINNER is used, if not, McCoy's INTLIFT and McDrag are used.
Standard Conditions at Altitude
When checked, the temperature, pressure and humidity for standard atmospheric conditions at the entered altitude (always 0% at standard conditions) are entered in the calculation. The standard used is the ICAO standard atmosphere.
Temperature
The measured or estimated air temperature.
Total Length
The total length of the bullet from the base to the meplat.
Transverse Moment of Inertia
The moment of inertia about an axis perpendicular to the bullet centerline, through the center of gravity.
Twist Direction
The direction of barrel twist when looking down the barrel from the chamber to the muzzle. A clockwise twist it "Right", a counterclockwise twist is "Left".
Vital Zone Radius
Radius of the vital zone for which the maximum point blank range is calculated. The vital zone is defined as the area from one radius below the line of sight to one radius above the line of sight.
Wind Angle
Angle of the wind direction. A North wind has an angle of zero, an East wind, 90 degrees, a South wind 180 and a West wind of 270 degrees.
Wind Speed
The speed of the wind.
Zero Height
The height of the zero point at the zero range.
Zero Offset
The lateral displacement the zero point at the zero range.
Zero Range
The range at which you wish the bullet to cross the line of sight.

Output Data

Atmospheric Density
The calculated density of the air.
Azimuth
The angle that the barrel makes with the line of sight in a horizontal direction -- positive to the shooter's right. This is the "lead" angle in minutes of angle for the selected zero range.
BC
The ballistic coefficient calculated using the drag function you selected.
CD
Drag coefficient.
CD&alpha2
Drag coefficient, second derivative.
Clα
Lift coefficient
Clρ
Spin damping moment coefficient
Cmα
Pitching moment coefficient.
Cypα
Magnus force coefficient
Cnpα
Magnus moment coefficient
Drop
The distance above or below the line of sight. Listed in either inches, minutes of angle or mils (6400 mils per 360 degrees or 3.375 mils per MOA). Drop is positive above the line of sight and negative below the line of sight.
Elevation
The angle that the barrel makes with the line of sight in a vertical direction. This is the "holdover" angle in minutes of angle for the selected zero range.
Energy
Kinetic energy of the bullet. The kinetic energy is a measure of the maximum amount of work (force time distance) an object can do. [It is also a measure of the work done by the firearm/case/primer/powder on the bullet.]
FF
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 drag function.
Mach Number
Mach number for the given velocity and atmospheric conditions.
Maximum Point Blank Range
Maximum range for which the bullet does not go above or below the maximum point blank range radius.
Maximum Point Blank Range Zero
Zero range to achieve the maximum point blank range.
Range
Distance from the shooter along the line of sight.
Range at Max. Height
This is the range at which the bullet reaches its maximum height in the vital zone when doing the maximum point blank range calculation. This is NOT the maximum height of the bullet for the trajectory calculation.
Sectional Density
Bullet sectional density
Stability
Stability factor for the bullet at the given velocity/range. It should be greater than 1.0 to ensure stability.
Speed of Sound
The calculated speed of sound.
Time
The time of flight of bullet in seconds.
Velocity
The speed of the bullet in feet per second.
Windage
The distance to the right or left of the line of sight. Windage is positive to the shooters right and negative to the shooters left.