Can a coil gun be made with a boost converter instead of caps?
A coil gun lives on the current flow.  A capacitor can deliver hundreds of amperes - though for a very short time.

The short time thing is important.  You need a pulse that starts, accelerates the slug, then dies before the slug reaches the point in the coil where the magnetic field would start decelerating the slug.

A boost converter that can deliver current pulses high enough to do any good is the diametric opposite of simple and cheap.

Using a mechanical switch for that kind of thing is the next best to useless.  If you do it by hand, you'll never get consistent results.  The current would probably weld the contacts of any switch you could come up with.

So, there are plenty of good reasons NOT to use a boost converter - at least not the way you are thinking of it.

Any coil gun you build uses something to generate a high voltage to charge the capacitor - a form of boost converter, if you will.  So in that sense, all coil guns use some form of boost converter.



Lets rephrase that:

All coil guns use a boost converter of some kind.  They (slowly) charge a large bank of capacitors because a boost converter that could charge them quickly wouldn't be cheap to build.    A boost converter that could deliver the current needed to drive a coil gun directly would be insane - and probably incorporate a capacitor as big as the typical capacitor banks used in coil guns anyway.