Coilgun - Measuring efficiency and speed with 3 different coils

In this video i am testing 3 different coils. All coils are 30 mm in length, i found this length most optimal for my projectiles.
I am testing coil with 250 turns, 350 turns and 450 turns. All coils are winded with 0.5mm copper wire.
Projectile speed is measured using optical sensors and kinetic energy is calculated using speed and mass.
Song: Abstract Electronic For Drift by Alexi Action (No Copyright Music) / Ghost

[@thawatchaichuanprasit915]

Great video!

[@doubleooh7337]

This is the problem that gives the 5% efficiency only The only difference I'd make Is wind
EVERY LAYER the same direction,
so the magnetic fields of each layer would be
n/s, n/s, n/s, n/s, n/s
You've wound it back and forth,
so you're magnetic field of each layer will be
n/s, s/n, n/s, s/n, n/s
Do you see how they'll give totally different results? It PUSHES the magnetic field outwards through repulsion,
Winding back and forth PULLS the magnetic field inwards through attraction within the coil layers itself
Hopefully you might try a side by side,
for others to see as that's one comparison not done yet ;) definitely 2-3x stronger

[@TONiT3CH]

second - may several varying coils be more efficient than 1 "universal" coil at/for certain stages?

[@simplecad7462]

I think you are correct. I will probably try multi stage coilgun next

[@TONiT3CH]

@@simplecad7462 Don't quote me on this, but for coil gun application I think cone shaped coils may better overall than perfect cylinder - coils.