So the other agents in the car never said Hickey did it? I think that's what is called a cover up.
Your claim, your burden of proof. Everyone near Hickey, including Hickey, testified under oath that no weapon was discharged from that car. If your claim is that they were lying then you need to prove they were lying -- not just suggest they might be.
How could you say "absolutely no evidence"? Ignoring it doesn't make it disappear.
Make
what disappear? Donahue's wild inferences and speculation?
Putting quotes around ballistics expert doesn't make the things he said false.
Removing the quotes doesn't make the things he said true. Thankfully we have means other than punctuation to determine whether his claims are credible.
First, "negligent discharge" is something people are specifically trained to avoid if they must use firearms as part of their jobs. It starts with ingrained practices as simple as keeping the safety on and your finger on the trigger guard until you've actually sighted the target. These moves are practiced until they are second nature. Hence for me it's immediately non-credible to suppose that a USSS agent on Presidential protective duty is going to have such poor firearm skills.
Second, the "smell of gunpowder" argument has been addressed here at length. Modern propellant, fired in an open area, doesn't leave an odor. But it's commonly believed among layman that it does, hence authors take advantage of it. What
does, however, make an odor is the exhaust from big heavy cars with big engines that are suddenly gunned in order to make a quick getaway.
Third, HP ammunition was not a thing for the AR-15.
Fourth, the trajectory "analysis" based on Donahue's concept of the head wound is comically presumptive, and provides no error analysis. This is important in science, but layman wouldn't know to look for it or care about it.
Fifth, Donahue simply lies blatantly that the long, round-nosed bullets that were the original Carcano ammo don't leave fragments. They do, in skulls, and such was demonstrated. But he ignores this because his hypothesis needs the head shot
not to have come from the Carcano. This leads into...
Sixth, the uncontested cavitation in the President's head wound is a characteristic effect of long, narrow, heavy rounds that exhibit minimal fragmentation. A high degree of fragmentation does not result in cavitation.
You writing extensively about something doesn't make it true.
It does, however, make it relevant if I happened to have already answered a point you raise. But if you're not interested in all the ways Donahue has led you by the nose, then we can't help you.
By the way, I apologize to you for being somewhat deliberately obtuse about the photograph and the rifle. That was unfair of me. I simply wanted
you to present your case and not make us guess at it.