He didn't come at it from that direction. Chambers is talking about
terminal ballistics, meaning wound ballistics. What could have caused
such a massive wound in the head? In his opinion only a ultra high
velocity projectile having the failure impact of a frangible bullet. We
know from combat experience the AR-15/M-16 .223 FMJ has that same problem.
The high thermal loads on the bullet due to friction down the barrel and
air friction on the way to the target causes the jacket and lead core to
soften and split on contact with hard bone. This happens with such
frequency that international pressure groups want the M-16 banned as a
weapon producing frangible bullets, a violation of Geneva Convention
protocol. The slower velocity Carcano 6.5 FMJ does fail and crumble when
impacting hard bone but usually into a few medium size fragments, rather
than a "lead snowstorm" of tiny fragments. Not impossible for the 6.5 mm
projectile, just extremely rare.
The fact a bodyguard in the follow-up car "10 to 12 feet" behind the
Limousine had an AR-15 in his hands during the ambush on the motorcade
makes it a prime suspect for a friendly-fire accident. Donahue came to
the conclusion the trajectory, entrance wound, and terminal ballistics all
pointed to the AR-15 as the source of the head shot. He was convinced the
bodyguard didn't even realize he fired this weapon at the time. Had this
SS Agent not lost his balance he might have shot the sniper in the 6th
floor window and been a national hero. As fate would have it, he may have
accidently provided a coup- de-grâce to a severely wounded President.
JFK died a hero with dignity while under fire. There is no doubt this
President who lived life with such vigor and joie-de-vivre would rather
die on the spot than waste away in a hospice.