I have printed rocket motor with 50% of PLA filling.
Nose cone - 100% filling PLA.
Drilling conductor (it's not a part of completed rocket) - 25% filling PLA.
Nozzleless rocket motor has 26 mm inner diameter and contains ~135 g of sorbitol rocket candy propellant (after drilling hollow core). Hollow core has 8 mm diameter and ~170 mm length.
This is not full instructions how to make rocket. You also will need appropriate rocket propellant and right ignition system. So, be careful and read relevant information before any try!