The magnetizing force is proportional to

Ampere Turns per Inch. You do not have

to know the Inductance of the coil.

Herb

The magnetizing force is equal to the amp-turns per _metre_ by definition, use SI units !!

Flux density inside a solenoid is B = µH, where µ is the permeability and H is the magnetizing force in A/m. (yes I know it looks like microhenries but this is an equation not a value!)

The coil is about 4cm long with 360 turns carrying 5A. Therefore H = 5 x 360 / 0.04 ~= 45kA/m, and since

µ0 = 4π*10^-7, B ~= 56 millitesla

The electromagnet formed on an iron core has a far higher permeability due to the iron, the field could be upto 2 tesla max (saturation point of iron).

Pwoerful coil guns need high flux densities, only achievable by pulsing very high currents from a high voltage capacitor through a coil of fairly low inductance - more turns will not help, more volts will. There are various dangers in constructing one, ie high voltage, exploding contacts and wires, projectiles.

Less powerful ones can benefit from iron cores as the peak magnetic field is lower, but the high inductance will limit speed attainable.