> If we assume nRT is a constant c then P = c/V.
> If we let c equal the chemical reaction of the propellant and call it 1000;
> then for a .300 cal that has traveled 5” down the barrel, P = 1000/(.300Pi*5) = 210
> for a .458 cal P = 1000/(.458Pi*5) = 140

The volume of a right circular cylinder is V = hPi r^2 (height times Pi times radius squared). The calculation then yields
30 cal: P = 1000/5(Pi*(0.154)^2) = 2684
45 cal: P = 1000/5(Pi*(0.229)^2) = 1214

Take care, Tom