The ball detent should be located somewhere near where the balls fall into the gun from the loader. It'll look like a little black rubber nub and it's primary purpose is the stop the balls from rolling too far forward. Usually, you can stick your finger down the feedneck and feel them. (Please do this with the air off your gun and the gun turned off!)
If it's not there, you can get replacements, or upgrade to what is called a "Timmy detent" which is the same thing, but a bit stiffer.
Never argue with an idiot; they'll drag you down to their level and beat you with experience." ~ Anonymous