If you read the linked article I posted, it goes through the entire "system", including identifying the caliber.
When a person dies from a gunshot wound, the investigation of the death falls to the local medicolegal death investigation system.
In a large urban setting this is usually a medical examiner's office, headed by a chief medical examiner and staffed by forensic
pathologists who have completed specialized postresidency fellowship training. In other jurisdictions, the responsibility belongs
to the elected coroner and his or her designated forensic pathologist. Distinguishing among accidental, suicidal, and homicidal
gunshot wounds; estimating range of firing; and distinguishing exit wounds from entrance wounds are critical skills and just a few
of the reasons why a forensic pathologist must be an expert in interpreting gunshot injuries. An error in any of these determinations
can have far-reaching consequences for the family of the deceased, the accused, the legal system, and the forensic pathologist.
This article seeks to lay basic groundwork for understanding the pathology of gunshot wounds.
A forensic pathologist does not have to be a weapons expert to interpret gunshot pathology correctly, but, because bullets fired
from handguns and rifles produce gunshot wounds, a forensic pathologist should at least be familiar with the nomenclature and
operation of commonly used guns and ammunition. The examination and interpretation of firearms and bullets is termed ballistics
or firearms examination. It is a separate field of expertise from forensic pathology requiring specialized training and instruments
of its own.2 The basic functional unit of a modern round of ammunition is the cartridge.
Even if a bullet has fragmented, a ballistics expert may be able to determine the caliber of the bullet from the aggregate weight of
the fragments. It is also extremely important to recover any jacket fragments whenever possible because in jacketed ammunition,
the rifling marks appear only on the jacket. Unless the jacket is recovered, the bullet cannot be matched to a particular gun. The
forensic pathologist must always remember that the chain of custody for any bullets begins in the autopsy suite. If potential evidence
is mishandled in the autopsy suite, whether by the pathologist performing the autopsy, technicians assisting, or the investigators
assigned to case, it diminishes the likelihood of that material being admitted into evidence at trial. Recovered bullets and fragments
should be photographed next to a scale identifying the anatomic location from which the bullet or fragment was recovered. Each
bullet and/or fragment should be then be sealed in a separate evidence envelope with the subject's name, the date of recovery, and
the name of the pathologist who recovered it written by the pathologist in his or her own handwriting on the envelope.
Even though the medical examiner is likely not the same person as the ballistics expert, the evidence is collected and provided to whomever is doing that part of the analysis.
Just like a medical examiner submits blood and tissue samples to a lab for testing, so will he submit jackets, bullets and fragments for testing.
Quibbling over whether the doctor himself runs every test personally is pointless.
But, a real
doctor would already know this.