T1 is trafo step down 18 volts 1 amp A.C. When Rectified and smoothed, this provides 25.2 V DC for electromagnets L1 to L4. Resistors R4 drops 12 V to obtain a supply voltage low enough for IC1 and IC2.
Most Crucial to the effectiveness of the gun are the setting of VR1 and the positions of electromagnets L1 to L4 on the copper tube (the values and measurements shown are merely a guide). Firstly, with L2 to L4 disconnected, VR1 should be tuned and L1 positioned for optimum effectiveness (place a wire inside the tube to feel how far the slug jumps with L1). Then L2 (now connected) should be positioned for optimum effectiveness (the slug will now exit the tube). Repeat with L3 and L4.
Electromagnets L2 to L4 were each found to substantially increase the range of the gun. In a forthcoming edition of SPE, the author will describe how readers may land a small projectile on Mars.