Jammer Six, if you can find any court case where analysis of GSR from factory loads has been used in evidence (and I'm pretty sure you can), then you can infer that the ability to introduce defense expert witness testimony on GSR might be important.
Handloads used in a clear-cut, black and white, observed by multiple witnesses or caught on security camera shooting aren't going to be questioned.
It's the grey area, conflicting testimony and uncertain evidence instances where this could become critical.
I can't think of a case where I've been kicked in the groin by an NFL punter; I can't think of a case where anybody has been kicked in the groin by an NFL punter. I am pretty sure we'd all infer that such would not be fun.