Actually, this is how this started.
My attorney client wanted me to find an expert on guns and we started talking about the case. He wanted someone to evaluate the status of the rifle (working order, trigger mechanism, etc.) and as we talked I realized that wasn't at all where the case's fulcrum was.
The case hinged on whether the defendant's gun shot at the floor first, or at the victim.
If at the floor, then no murder.
Thus, my questions.
We haven't ruled out any experts. It's just that the target (excuse the pun) needs to be calibrated.
To learn about .223 ballistics, I recommend you GOOGLE Beltway Sniper Ballistics and read everything written about this subject back when it occurred.
Another thing you might want to consider is the rifle’s firing pin. If this rifle had a free floating steel firing pin as most do, the firing pin could have detonated the cartridge primer when the bolt was released, as commercial .223 has softer primers than military 556 primers. I once saw this happen inside an aircraft when a man using commercial hollow point .223 and a steel firing pin in his M-4 charged his weapon slightly before he departed the aircraft and put a hole through the aircraft’s floor. Needless to say that really pissed off the pilot.
If your shooter used a rifle with a steel firing pin and commercial .223 ammunition, an accidental/negligent discharge could be an alibi.