Well, there are literally zero true, full-spec and proper .357 Magnum loads that have ever used 1, 2 or 3 grains of powder.
Starting at it's most basic (as we have no idea of your level of knowledge or your intent) it first makes sense to note clearly that in this endeavor, a "grain" is actually a standard unit of measurement. So simply to be clear, a grain isn't a "granule" or a piece of powder, it is a weight measurement whereby 7,000 grains equals one pound.
Full-spec .357 Magnum (properly!) uses a powder that is a bit slower with regards to burn rate, relative to other handgun ammo. While a target level load might use a faster powder and 5-6 grains of it, a "late 70's Winchester metal piercing 158gr" case would typically use a slower burning powder and MUCH more of it, such as the 15-17 grains mentioned in a post above mine.
Commercial ammo typically doesn't use the same powder that handloaders can purchase. They tend to use HUGE lots of powder that they alter to do specifically what they want that powder to do. They don't read a load recipe from a book like many handloaders do, they load a charge and test it and alter things from that point to get the result they desire and they do this in controlled laboratory conditions with a bankroll that exceeds the handloader's typical net worth.
And in the 1970's, they had much more primitive equipment and it is likely that they didn't have nearly the full idea of what they were making and selling nearly as well as they do these days.
Often we will have an author show up at the forum to ask questions similar to yours so that he can write something in a fiction novel that will read well even to those select few that will appreciate the level of detail. The general audience here include exactly those kinds of folks and nobody has ever minded these kinds of questions and are happy to help.
But the process tends to run more smoothly when the person who asks the question gives some sort of background or goal behind the question. Otherwise, to many of us, it reads as if perhaps some neophyte might attempt something downright dangerous using poor research.
