Have you ever researched the type of wounds from 6.5 mm rifles inflicted on Allied soldiers during WWII? There were relatively-"clean" through-and-through soft-tissue wounds as well as devastating hard-tissue head wounds.
That's air in the missile passage. It compromises the opacity of bone. The calvicle and ribs are weak on X-ray because of air.
Opacity of bone is a matter of bone density and thickness. Ribs are not really thick so they don't absorb xrays well when perpendicular to the xrays. When at an angle to the xrays they present more bone to the xray path so they block more, which is why the ribs at the sides are more opaque than the central parts. So although the opacity of the ribs is weakest where the lungs are fulllest, it is not because of air. Air doesn't affect the bone's opacity.
You fail to appreciate the difference between how bullets of this type impact soft vs. hard tissue.
The bullet destroyed 10 cm of rib. According to you it was still travelling at 1700 fps when it struck the 5th rib. According to you it did not strike nose-first. According to Larry Sturdivan the jacketed 6.5 mm bullet will deform if it strikes bone at a much lesser speed nose-first and even lesser still if not nose first. And that is just striking the rib. Then there is the radius, which is a very hard bone. Do the irregular holes in the shirt cuff really look like they were made by CE399?:
