I was a competitive shooter for several years. Competing requires lots of practice & ammo is expensive, so - like most shooters - I handload.
For those unfamiliar with it, handloading means re-using the most expensive part of a cartridge - the brass shell casing & replacing the primer, powder & bullet, which are purchased separately & using a press & various tools to assemble everything. That reduces the cost by 50% & enables more practice.
Example: A 50-round box of factory 45 ACP can cost $25.00. I can handload it for around $9.00. And I can choose the powder, primer, & bullet that provides the best accuracy in my particular gun. Since I'm not loading for profit (like a factory production), I can take more time & be more picky.
It's sort of like cooking. You can buy a cake at the store, or you can buy flour, sugar, butter, eggs, etc. & make your own cake. And you control the ingredients, quality, taste, etc. If you're really good at it, you can make a better cake than you can buy. And you can probably make more than one cake for less money than buying one ready made.
"Win231" (short for "Winchester 231) is one of my favorite powders. (actually, modern gun powder isn't really gun powder; it's classified as "Propellant" because it doesn't explode; it just burns (fizzes like striking a match).