If left unharnessed, the inductor will toss the iron core completely out, hence the railgun analogy.
E=BLV
E=volts
B=Magnetic strength in Gauss
L=Length of conductor (your coil, proportional to the number of wraps)
V=Velocity of magnet through the coil
You usually know three and solve for the unknown.
More wraps on solenoid wire and the stronger the magnetic field, the higher the velocity of said core through the windings, and the greater the pulse, or voltage in this case.
The key is the explosion that creates the huge velocities of a magnet through a winding with mucho windings count.
I recall this stuff from physics in college. I remember thinking if you could load a gun with a strong magnet as a bullet instead of a typical lead projectile, this would provide your mucho velocity. Then you just fashion a coil that attaches to the muzzle and send the magnet through with normal rifle casing.
In this case, I'd choose a rifle and fashion my own bullets out of magnetic material or, use a shotgun slug, drill a hole in it and put a magnet inside the massive hollowpoint you just fashioned. Or, you could machine the magnetic bullet under sized and wrap it with paper to engage the rifling adequately.
In a rifle that had screw on tip for a flash suppressor or silencer, you could fashion your coil out of something aluminum that you could wind with 1000s of wraps of magnet wire, the more the better. This is the L portion of the equation. Now, what kind of antenna do you connect it to direct such pulse, I don't know, that's beyond my field. I was a mechanical engineering student, not an electronics guy. However, were I attempting this, I suspect I'd use one round at a time. The pulse might be intense enough to ignite any primers in a magazine. I'm not sure, for they should be grounded, but I wouldn't chance it. In the case of the firearm mounted model I just discussed, it would not be destroyed each time, so only your bullets would be consumable, everything else should survive. If it created too much amperage, it could fry the wire, in which case, you'd need heavier gauge wire and need to try again.
Good luck.
I suppose some electronics gurus should be chiming in here. I remember an electronics major buddy doing impulse calculations where they dumped the energy out of a capacitor at nearly zero time and it generated huge spikes in electrical energy. I don't recall if it was current or voltage, but I suspect voltage.
Hope this helps. Have fun and be safe.
jeepmor