Python Paintball, Give Your Balls A Squeeze
Sorry, man. I use one of these kits every day, and am planning to buy more soon. They even have a lip on the front of every insert that keeps it from coming out for any reason. Out of all the barrels I've ever used, this one combined with a .686 DYE Classic has been my favorite for months now. In fact, I read not too long ago that Cockerpunk uses the exact same combo.
Oh, the Python ones are also made of aluminum, which I think I would prefer by all accounts. Some of us folks are a bit too hard on our barrels, no matter how hard we try.
I also have a barrel bored out to take a Python insert in reverse. The lip still helps, since it gets trapped between the barrel and gun body.