I have never believed this.
For one thing, this gets bandied about without a single court case to back it up. I've asked others for the case: no one seems to know.
Difficulty in establishing residue patterns? This insults the crime-lab folks, who know their craft and science very well. Besides, factories change powder and amounts in the same loading all the time. The box of .38 Special jacketed hollowpoints you bought yesterday very likely is not loaded with the same powder loaded 10 years ago.
Providing you reloaded with a bullet typically commercially available (no homemade mercury-tipped, exploding, fragmenting, etc. bullets), you will be judged on the legality of shooting, not what you fired.
Of course, any prosecutor will try to distract the jury by mentioning you used hollow points, a "Magnum" (even if you had it loaded with .38 Specials), etc. But these issues will be addressed even if you used factory ammo.
Whether you had the legal right to shoot another person will be the crux of the issue.
You MUST prove that you had reason to believe that you were in fear of:
1. Death to yourself or others.
2. Permanent, debilitating injury to yourself or others. Note, the injury must be permanent and extremely grievous. If someone comes at you with a baseball bat, you would have reason to believe that the bat could cause you death or permanent, debilitating injury. But if that same person came at you with a shoe in his or her hand, you likely shouldn't shoot.
There are other factors that play into shooting in self defense:
Your physical condition An 80-year-old man in a wheelchair could probably shoot someone armed with a shoe, or even bare fists, if they threatened to beat him.
But ...
A 20-year-old man in good physical condition facing another 20-year-old armed with a shoe? He'd be in trouble for shooting.
It all comes down to -- Did you have a reasonable belief that your life, or the lives of others, were in danger, or that you or them would suffer serious, debilitating, permanent injury?
Don't use reloads or you'll be in serious trouble with the prosecutor? Show me the court cases.