No experience with the Jet bullet but the Barnes original came in two or three jacket thicknesses .30", .35" and I think .40" but maybe thicker. The last ones were designed for the .375 H&H and could be what your son used accidentally. The other thing is the jackets didn't have much taper and on some bullets almost closed off the nose. With the right bullet they perform well, if I wanted more expansion I would hollow point the bullet.
