When I was playing around with coils and caps, I was using a coil of about 100 turns and a couple of 39uf 8Kv capacitors. An aluminium ring from an old hard drive placed on the end of the coil was repelled with astonishing force, but an old spanner was only thrown weakly. It seems that there is a conflict between the repelling effect caused by the current induced in the projectile and the magnetic attraction of iron. I would suspect that a number of slots cut in the projectile would reduce the induced current,and allow the magnetic effect to be more in evidence. Try chucking a bit of ferrite! The coils you are using with many turns will have a much higher inductance, and the accelerating pulse will last much longer. The current in the projectile will also be much less. Hope this helps