Cover a table with a tarp to protect it from any paint that might drip or leak. Place a pitcher on the table and pour the paintball paint slowly from its container into the pitcher. Put the pitcher aside.
Stretch four to five water balloons to make them easier to work with during the filling process.
Insert the tip of a plastic funnel into a balloon's opening. Slowly pour the paint from the pitcher into the funnel so it does not spill. Fill the balloon about three-quarters full.
Remove the funnel from the balloon and tie the end of the balloon to close it. Make sure the knot is tight to prevent paint from leaking out. Insert the paintball into the paintball gun to see if it fits. Paintballs that are too large will break inside the gun, while paintballs that are too small will not shoot properly. Adjust the size of the paintball, and repeat the steps to make additional ammunition.