A couple old errors came up in this thread. First, pressure is only half the equation. While the 9mm Luger and .40 S&W might generate similar pressure, by virtue of the larger case hear the .40 imparts significantly more pressure to the breech face (bolt thrust). If both cartridges generate 35,000 psi the 9mm will deliver 3,464 lbs and the .40 will deliver 4,398 lbs - a 27% increase. The .40's larger case will also generate more radial pressure and more hoop stress which can also be magnified if the larger bore is cut into a 9mm barrel.
Second, a heavier recoil spring does little to nothing to decrease unlock time and that is being generous.
