Contents - Index - Next


Determining and Defining Bullet Parameters


Old Panel



New Panel




When entering a new record, the Bullet Length and In-Case fields are required fields for the calculations and must be entered as the last two entries in the 12 entries of the  sequence.

After the Bullet Length Field value has been entered and the field is exited, if the In-Case field is blank, the bullet in-case length will be automatically calculated as approximately 50% of the bullet length. You must first exit the In-Case field before that value may be edited.

When the In-Case field is exited while entering values for a New Record, all remaining values will be automatically calculated.

After the remaining values are calculated, the In-Case field may be edited to any reasonable value without causing an error.


Calculate the Bullet Stability Factor


The Twist Rate, Muzzle Velocity, Stability and Calculated Bullet length field value entries are optional. They may be used to calculate an optimum bullet length that is appropriate for the caliber and useful muzzle velocity of the application.

When entering the twist rate, enter only the value that signifies the distance of the twist rate.  If the value is 1 turn in 16 inches, then enter the value 16.  Do not enter a value such as "1/16" or "1 in 16".

The Bullet Stability Equations of Don Miller that include muzzle velocity, bullet length, bullet weight, twist rate and a stabilization factor have been adapted to calculate each one of the factors if all three of the remaining factors are known.

The minimum calculated stability factor to stabilize a bullet has been determined to be 1.5, However the minimum safe factor is usually considered as 2.5. Therefore a default value of 2.5 is used as the starting factor in the calculations.  

The Bullet Weight in these calculations is taken as the calculated casting weight and remains constant during the calculations.  If a new bullet length is determined, it should be set and then a new weight calculated by clicking the    button  at the bottom of the form.

The equation used to calculate the Stability Factor of the bullet is:

SF = Stability Factor.
G  = Bullet weight, in grains.
D   = Fired Bullet Diameter or Caliber.
T   = Twist Rate, in calibers.
L   = Bullet Length, in calibers.
V  = Muzzle velocity, in f.p.s
SF1 =  30 * G    T     D  L    (1 + L );

The stability factor SF1 is based on a muzzle velocity of  2800 f.p.s. and the equations use this formula to modify the stability factor as it is affected by the applied muzzle velocity:

SF = SF1     [  V    2800 f.p.s ]  

.  
A muzzle velocity that is below Mach I is adjusted to Mach 1 (1120 f.p.s.)


If the bullet length and the muzzle velocity are known, then enter those values and click  the button to calculate the twist rate.  
This formula will be used to make the calculation:

SF1 =  30 * G    T     D  L    (1 + L );

SF1 = SF *  [  V    2800 f.p.s ] 

T  =  SqrRoot [ (30 * G)    SF1    D  L    (1 + L ) ];


If the barrel twist rate and the bullet length are known then enter those values and click  the    button to calculate the muzzle velocity.  
This formula will be used to make the calculation: 

SF1 =  30 * G    T     D  L    (1 + L );


Cube root of 2800 is 14.094597

V :=  ( SF1 * 14.09459  SF )


If the barrel twist rate, stability factor and the muzzle velocity are known then enter those values and click  the    button to calculate the bullet length.  
This formula will be used to make the calculation: 
Solving for L in the formula shown below requires finding the solution of a cubic equation and involves a process too advanced to be detailed here.

SF1 = SF *  [  V    2800 f.p.s ] 

L   +  L  =  30 * G    T     D   SF1


If the barrel twist rate, muzzle velocity and bullet length are known then enter those values and click  the button to calculate the stability factor of the bullet.
These formulas will be used to make the calculations.

SF1 =  30 * G    T     D  L    (1 + L );


SF = SF1     [  V    2800 f.p.s ]  



Copyright , TMT Enterprises 2012