It must be the advertising hype. Otherwise, how could so many shooters get so much wrong information, or lack of information, on primers!
If primers are tested in a lab, some will show more, and/or longer, fire than others. Usually it is the magnum primers that show as being the hottest.
But in real life, there is no real difference between standard and magnum primers, either in rifle or pistols. That is, a hand loader is unable to detect which primer it is, that is in his cartridge.
Some will say that you "Must" use a magnum primer with powder such as H4831 and some ball powders. Let's look at the facts. War surplus powders, including H4831 and the various Hodgdon ball powders, were on the market and hand loaded very extensively, for fifteen years before magnum primers were invented! IMR ball powders had been around a lot longer than that, all being lit with standard primers.
When magnum primers came along, we tried them. And since then I have used them interchangeably in rifles and in 357 and 44 magnum revolvers, and have been unable to detect any difference in the loads, of whether they were fired up by a standard, or a magnum primer.
I have chronographed identical, hot loads, of both rifle and revolver, and was unable to tell by the chrono results, which loads had the magnum primers in them.
Oh well, it gives lots of discussion on the gun nutz!