Coil-Gun

Many years ago, I designed a coil-gun (the principle is illustrated on the right). It was a popular design, although as it stands it needs small but significant improvements (see below). My original design is at Magnetic Gun. The reason for this post is that, at the moment, a student is building it as a project, and is close to the exciting (or terminal) switch-on. OBSERVATION: When my design was first published, it may have been the only hobbyist design "out there". My usual publishers would not publish it, for safety's sake -- but it is harmless. The original design really needs a Zener diode in place of R4. There are ways, too, in which one could greatly beef it up: among other things MOSFETs in place of the bipolar transistors, a magnetic slug, and separate capacitors for each MOSFET.