....am interested in learning if there is truth to this. Is there any definitive legal proof of this (i.e. a court case that someone can cite) actually happening?
Doesn't matter. The key issue is one of the admissibility of evidence.
In law, it doesn't matter whether a trial court case involved self defense, suicide, poison, counterfeiting, arson, odometer roll-back, rape, falsification of records, quality control issues, or whatever. What counts is the ruling of an appellate court on what kind of evidence or expert testimony may be allowed and why.
The issue of admissibility is a very complex one, and the nuances are far beyond what can be explained in a short internet posting. One can take a several hour course on the subject, but it would mean little without a good foundation in basic legal philosophy.
Should a defendant's case depend on whether gunshot residue evidence supports or contradict his testimony or that of someone else, it may become necessary to introduce test results and supporting expert witness testimony. Should the judge not allow it, the jury will never know about it.
The short answer is that one does
not want to have to rely on the admissibility of evidence that one cannot have independently verified by someone else who is not a party to the litigation, and that was not created and maintained under rigorous. documented procedures.
That would include, among many many other things, handloaded ammunition.
Perhaps this will help.
I do not carry hand loaded ammunition.
