Test Projectiles
Several
sets of test projectiles have been constructed as detailed below. The projectile
lengths have been set to equal the test coil length of 25mm and are radiused at
the front end. The projectiles are machined from free cutting mild steel bar.
The powdered matrix projectiles are made from filings of the same alloy. There
are four projectiles of each type. The reason for this is simply good experimental
practice. By using a group of test objects you can be more certain that the results
obtained are indeed typical of that object type and not in fact a statistical
anomaly.
Solid
Projectiles 
These
projectiles are simply solid steel rods. This is the most basic type of projectile.
Solid
Core Projectile Crosssection:
Solid Projectile 
Length (mm) 
Diameter (mm) 
Mass (g) 
SP1 
25.05 

9.40 

12.7


SP2 
24.90 

9.37 

12.6


SP3 
24.77 

9.38 

12.6


SP4 
24.85 

9.38 

12.6


Cored
Projectiles 
These
share the same profile as the SP's but have a hole running along their axes. The
purpose of the CP's is to study the effect of loading on the coil. In all cases
the core is drilled to a depth of 20 +/0.1mm.
4mm
Cored Projectile Crosssection:
Cored Projectile (4x20mm) 
Length (mm) 
Diameter (mm) 
Mass (g) 
CP41 
24.84 

9.36 

10.8


CP42 
24.96 

9.33 

10.8


CP43 
24.94 

9.39 

10.8


CP44 
24.70 

9.32 

10.7


6mm
Cored Projectile Crosssection:
Cored Projectile (6x20mm) 
Length (mm) 
Diameter (mm) 
Mass (g) 
CP61 
24.39 

9.36 

8.4


CP62 
24.99 

9.40 

8.6


CP63 
24.86 

9.39 

8.5


CP64 
24.86 

9.38 

8.5


Slotted
Projectiles 
Slotting
the projectile reduces the possible eddy current paths and so increases the dynamic
flux penetration. Projectile under development.
Slotted Projectile 
Length (mm) 
Diameter (mm) 
Mass (g) 
SP1 






Powdered
Matrix Projectile 
By
using a powdered core virtually all projectile eddy currents are eliminated. These
may give an insight into whether eddy losses are a significant issue in projectiles.
Projectile under development.
Powdered Projectile 
Length (mm) 
Diameter (mm) 
Mass (g) 
PMP1 
25.0 

9.40 



Ferrite
Rod Projectile 
Ferrite
offers a very high resistivity which almost completely eliminates eddy currents.
This type may prove better than the powdered matrix projectile in extremely fast
coilguns.
Ferrite Projectile 
Length (mm) 
Diameter (mm) 
Mass (g) 
PMP1 
25.0 

9.40 



Note
that ferrite is very hard and very brittle. The stuff is tricky to machine, I
managed to turn a projectile from a piece of aerial ferrite rod but it blunts
HSS lathe tools in a matter of minutes.
