AR Buffer System Theory: How to Select the Correct Buffer
SmallArmsSolutions has done a great video which demystifies the AR buffer system and gives some great advice of selecting a buffer.
Bottom line: If you got a gun with a buffer, think twice before you change from OEM. If you are building a gun, do some home work before you throw in an imported standard buffer. If you have a 9mm gun, buy a dedicated 9mm buffer. It is important.