In 1935 Smith & Wesson introduced the 357 Magnum. This was the entirely logical solution to the ballistic limitations of earlier 35-caliber revolver rounds. Loaded to very high pressure, original loads launched 158-grain bullets at 1500 fps, making it the first standardized revolver round that generated more energy than the original blackpowder 45 Colt round did. After about 1970, load pressure was moderated and ballistics progressively declined. Modern factory loads launch 125-grain bullets at about the same velocity as the original factory load launched the 158-grain bullet. The reason for this moderation of load pressure is good to keep in mind: many guns have been chambered for the 357 that are not as robust as the original S&W Model 27 was. The ancestry of the 357 Magnum goes all the way back to the 36-caliber Paterson Colt cap-and-ball revolver. When folks began converting that revolver to work with cartridges, they needed cartridges to work in the converted revolvers. The first of those was heal-based (externally lubricated like a 22 Long Rifle) with a 38-caliber case and named the 38 Colt. Importantly, the heal of the bullet was 36-caliber. Soon a longer round named the 38 Long Colt and internally lubricated hollow based loads were offered. Eventually, guns with smaller bores were designed to give better accuracy with those loads. The original load got a new name, 38 Short Colt (a retronym), then the longer-cased 38 Special came about the time smokeless propellants became almost universally standard for factory loads, with improved performance as a goal. A generation after the 38 Special was standardized, S&W recognized the need for a new round that would not chamber in older, weaker guns, so it lengthened the case, again, and the 357 Magnum was born. That was not the last of the progression. Silhouette shooters needed more momentum to consistently topple their targets, so the longer 357 Maximum was developed. It is interesting to note that the 222 Remington, progenitor of the 223 (5.56 NATO) is nothing more than a necked-down, rimless version of a lengthened 357 Magnum case. As such, the original AR-15 chambering owes its heritage to the, circa 1839, Paterson Colt 36-caliber cap-and-ball revolver. As with any revolver round, best practice is to apply a roll-crimp after seating the bullet. This helps to lock the bullet in place against chambering forces that might otherwise drive it into the case. I cannot too-strongly recommend getting a second seating-and-crimping die so you can have one adjusted to only seat the bullet and the second adjusted to only crimp the case mouth. Generally, attempting to do both operations in one step is a recipe for damaged and destroyed cases.