- What kind of slugs can a rail gun fire?
- How do I keep the projectile from welding to the rails?
- How does the sabot rail gun slug work?
What kind of slugs (projectiles) can a rail gun fire?
A rail gun can fire virtually any type of projectile, provided that a least some portion of it conducts electricity and makes contact with the rails. Home built systems often use quarters, washers, or ball bearings as projectiles. Mostly, these do not work, and just end up welding to the rails. Welding is the most common problem in home rail gun design, and is difficult to overcome using traditional methods. Some guns have used graphite projectiles in an effort to eliminate welding, provide lubrication, and increase rail life time. While solving the welding issues of more conventional types, these projectiles have several disadvantages: they are low density, and provide increased electrical resistance.
How do I keep the projectile from welding to the rails?
Welding is strictly a problem of current density and heat. Current density refers to the amount of current flowing through a particular portion of the circuit, and generally reaches its highest levels at the interface between the slug and the rails. The contact area between the slug and the rails must be as large as possible to keep the current density from welding the two together before the projectile can begin moving. In an advanced high power design, the projectile will ionize (can you say plasma?) due to the heat generated by the extremely high currents involved. The major difficulty in getting optimum rail to slug contact is the balancing act of projectile to rail surface are contact, aerodynamic stability of projectile, heat dissipation, and friction with rails. One solution to these issues, which results in exceptional projectile performance is the sabot round.
How does the sabot rail gun slug work?
The main interest in creating a weapon that fires a projectile is transferring muzzle energy to the target through momentum (velocity and mass). At the same time aerodynamic stability and drag and thus weapon accuracy and range are of concern. The sabot round uses a disposable case (sabot) to carry the projectile clear of the weapon barrel. In the rail gun case, the sabot allows the best of both worlds, allowing the sabot to be designed for optimum current carrying capacity and heat dissipation while the projectile itself may be designed for stability and drag. Recent efforts use an aluminum sabot cradle that carries a tungsten, fin-stabilized round down the rails and off into and through the target. The cradle must carry all or most of the current provided by the power supply and thus contact area is very important. In these designs, the power is provided by a compulsator and often results in the ionization and vaporization of portions of the sabot cradle. Tungsten makes an ideal metal for the projectile due: it's high density (19.3 g/cc) , hardness (31 Rockwell C), and extremely high melting point (3370 C). See figure 1 for a sample rail gun sabot design.
Figure 1 Sample Rail Gun Sabot
**Note, I have been informed that the use of multiple fins in the sabot casing has been found to result in non-optimal current distribution and eddying. Current designs utilize a single contact sabot cradle. (Thanks Ben!)
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Page last updated 4/24/02
