paul.nortness, I have an Estes Astron Scout from the 1970's and the engine retaining clip is longer than a standard engine. This is to shift the engine casing rearward ( center of gravity ) C/G at ejection, or deployment, for a tumbling lightweight recovery, without ejecting the engine casing. The clip should hang out some, but remain hidden inside the tube fin assembly. If your kit was not supplied with a BT-5, but a BT-20? The Astron Sprite was originally designed to fly with Estes 18mm Short Engine Series Motors no longer in production, they were an experimental rocket motor, like a thicker walled Estes Mini Series Motors. Install a Mini Engine Adapter 5/20, 13mm/18mm to launch. I prefer ejecting the motor mount, attached to the nose cone, with lightweight stranded Kevlar 3 feet long, so everything is recovered, it's lighter in weight, just add nose weight, if necessary and wadding. Hope this helps.