Why is there a gap between the thrust ring and the motor case on Pro38 motors?
This is normal. In production, there is some variation in the length of the propellant grains, therefore the total length of the propellant grain stack varies. The reload is designed to seat fully in the case with a gap of about .030″ between the thrust ring and the casing, if the grains are exactly the design length. If the grains are a few thousandths of an inch short, then the gap will be less. If they are a little longer, the gap will be more. Simply screw the reload into the case until it is snug but not overtight. If the gap is excessive (see instructions) disassemble the motor and check over the reload assembly. Reassemble.
