Previous techniques used "progressivity, regressivity and progressivity-regressivity rollover" coefficients for each propellant to explain the burn front progression. Naturally these coefficients are cartridge specific and not usable for any cartridge except the one for which the coefficients were generated. Performance predictions based on these coefficients for new cartridges are, in general, not acceptably accurate.
Utilizing the additional double burning area defined by the shear line caused by bullet movement makes a reasonable prediction of peak pressure possible. In fact iterative solution of the equations given below make it possible to calculate the entire pressure time curve for any cartridge of length greater than 0.6 inches and shoulder angle greater than 35 degrees.
We can predict cartridge propellant
burn rates from the classic solid rocket burn rate equation:
Br2=Br1 [P2/P1]exp N
Where: Br2 is local burn rate inside the cartridge
or barrel.
Br1 is test burn rate at test pressure determined by
Crawford Bomb.
P2 is local static pressure.
P1 is test pressure.
N
is burn rate exponent (less than one) over range of pressures being
considered.