What is the difference between .357cal and .38cal handguns?

Assuming we're talking about .357 magnum and .38 special revolvers, the most basic difference is a .357 magnum chamber is slightly longer than the .38. The .357 casing is also slightly longer than the .38 and holds more powder. The actual bullet (the piece of lead) is the same, but because of the higher pressure of the .357, the bullet travels faster and has more energy. .357 magnum guns are typically a little heavier than a similar gun in .38.