I believe the shallow back wound bullet is supposed to be the bullet that SA Paul Landis claimed he found inside the JFK Limo. Landis also claimed to have placed that same bullet on a hospital gurney.
Yes, it's too bad Landis didn't reveal his bombshell at the time. I will grant that the autopsy doctors' inability to trace the path of the bullet that caused the back wound is puzzling. I will grant Cliff Varnell's point that the alignment of the holes in the clothing with the throat wound is problematical (yes, I know all about the "bunching" argument regarding the clothes). Add in the condition of CE 399 for all the damage it is supposed to have done, together with Connally's insistence he was hit by a different shot, and the SBT is somewhat (or considerably more than somewhat) difficult to swallow. On the other hand, it's quite difficult to accept the back wound being a Carcano dud that found its target 80+ yards away and penetrated two layers of clothing and an inch or two of skin. In my past experience with reloading, in which I managed to create a fair number of duds, that isn't realistic dud performance.
I tend to think the SBT, with all its problems, is the most likely solution. There are so many variables as to EXACTLY how the rifle was positioned, EXACTLY what the particular cartridge was like, EXACTLY how the car was positioned and moving, EXACTLY how JFK's clothing was positioned (including the possible effect of his back brace), EXACTLY how JFK and Connally were positioned, and EXACTLY what the bullet did upon impact, transit and second and third impacts, for me to place much stock in forensic reconstructions supposedly showing the SBT is impossible. I do like to play around with alternative scenarios and am not convinced the SBT is absolutely essential to the LN narrative.
