HCR Repulsor

The HCR Repulsor is what I'm calling my attempt to build a hybrid coil rail gun.

HCR - Hybrid Coil Rail

Repulsor - Because the magnetic field is repelling the projectile, rather than pulling it.


Because traditional coil gun design is an open-air coil / sliding core, it is highly inefficient. If one could utilize a iron-core electromagnet in the generation of the magnetic field, efficiency could be drastically improved. My hypothesis is using an iron-core electromagnet paired with a non-ferromagnetic slug which has a magnetic field around it due to a large current passing through it will be more efficient than an open air coil pulling on ferromagnetic slug.

This repulsion-based design side steps several issues with tradition coil gun design:

  • Where to position the projectile relative to the coil (this ties into the below problem)
  • Timing issues with the capacitors being fully drained before the slug gets to the middle of the coil
  • No drag due to the (now magnetized) slug passing through the coil

Note: being the uneducated plebeian that I am, I have not actually done the physics/engineering calculations on this and could be very very wrong. I'm still trying to learn how to translate magnetic field strength (gauss/tesla) into force (newtons).


I have evidence showing that a magnetic field around the rail gun absolutely improves efficiency. This can be from permanent magnets or from coils. This changes my design a tad, but increases the likelihood of functioning.

Next Steps

I think the ultimate design will be rails and electromagnets–Neodymium magnets *might* be strong enough on their own, but I think a good coils design will prove much more powerful (and much cooler to look at and build).

Step 1: Bench Top POC

I need to prove for myself that the basic design works. I've been (for years now) getting caught up on making rails that will last a long time and be extremely functional–this has been stalling progress on this project. The benchtop model will be just good enough to work. It will use cheap steel for the rails, permanent magnets, and a benchtop PSU.


  1. Build a benchtop PSU (from a computer PSU)
    • Need old PSU, resistors, heatshrink tubing, terminals, LEDs, cool switch – most should already be kicking around

Step 2: Bench Top V2

Using the same rails and permanent magnet from step 1, but build a PSU and capacitor bank. Hopefully can deliver a higher-energy shot without ruining / welding the rails together.

See Also