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a 30 caliber running IMR 4895 at 47.5gr (55,000 psi) will net approx 2516 rounds before slipping into the next ring.
the same 30 caliber with IMR 4064 47.8 (55,500 psi) 3165 rounds before again slipping into the next ring.
The 7.62 mm NATO will net a higher count with IMR 4895 at 42.5 grs will be 3143 before slipping to the next ring. With IMR 4064 at 43 grs rounds count goes to 3911.
Why? simple we are not running these to the max pressure which causes more erosion, the more grains of powder the more erosion, the higher the kJ/kg factor the higher heat potentional again more erosion. The factors are:
a. Heat/ energy potential of the powder (kJ/kg)
b. amount of powder
c. pressure generated
d. rate of fire.
note I said accuracy slips to the next ring I did not say it (the barrel) was shot out. In the table above I used the 6.5 Remington mag at FULL pressure of the brass, then compared to 10,000 reduction.
Pressure = Velocity pure and simple.
if one was to say use the 30 caliber at full potential in say IMR 4895 53 grs that 2516 for 47.5grs drops to 1916 for the increased charged, what has changed is the amount of powder and pressure not the heat potential of the powder.