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.
Makes total sense. I never knew they made different jacket thickness's but obviously the H&H would need it. I saw that happen with a 358 Winchester last year on a bison hunt. The guy had loaded some 225s that were not made for 358 velocities. The amazing thing was that the first bullet took the bison off her feet. She never got up. We found the bullet and you could have reloaded it. No expansion at all, even on the nose.
