This is a drop-in replacement for the barrel of a Nerf brand Tech Target blaster. The standard barrel replacement is compatible with standard foam darts, simply push the darts into the barrel from the front. This works well with the stock spring, but is not recommended with an upgraded spring, as the high pressures will tend to damage stock darts. The standard barrel is compatible with half length darts, but requires a ramrod to fully insert them. With the stock spring, you can expect velocities of about 80fps. The CPVC insert compatible barrel is a receptacle for a CPVC barrel replacement. This is recommended if you are using half length darts and an upgraded spring. A 4" CPVC barrel is optimal, and you can expect velocities of about 140fps.