A thought.
You use your sidearm successfully in an SD shooting, say 6 feet distance. The perp and or witnesses say he was 30 feet away from the actual spot from which the action took place. I take it a GSR test would prove something regarding this aspect. The ammo you have in the firearm and any other of same type in your possession cannot be used to test as it's evidence.
Your handload with your choice of projectile and X amount of YZ powder was used. Will the defense have someone load rounds for testing? Does the prosecution?
Or ABC factory ammo was used, the same or similar lot of ammo procured from the factory for testing. No guess work there.
This is my understanding of what could happen. If you live where the firearms are highly regulated and use and carry are scrutinized does it make a difference? Without a gummint study I thinks it's fair to say the around half the citizens of this country live in restricted areas. What's truly a fair answer?
I carry factory ammo for that purpose. The FBI load worked well enough for a few decades and has a track record. If I'm carrying a 1911 it will be a popular factory HP round, with a good history. Both have been used by LE for sometime, that could be a benefit.
Does this sound reasonable, if not please tell where it may be wrong.