Retention Bolt

The projectile’s starting position is critical. The position must be repeatable, adjustable in small increments, and provide positive retention with low separation force.

Retention Bolt

This coilgun does not need a magazine loader; manual loading is acceptable for my purposes of coilgun demonstration.

A lightly magnetized bolt satisfies all the requirements. The threads allow easy adjustment in small well-defined amounts. A small permanent magnet placed at the head end provides a small but sufficient force on the projectile. No glue is needed; the magnetization holds it securely in place.

This carriage bolt is approximately 3” by ½”, it has a thread pitch of 18 turns per inch. It can be adjusted by 0.0555 inches (1.411 mm) with each turn.

A small rectangular magnet at the end away from the projectile was found to work very well in lightly magnetizing the bolt.