The use of a single coil design is more favorable over a multiple coil design.  The advantages of a single coil are smaller size, weight, and lower cost.  However, a single coil has a point of diminishing returns, and just where those benefits end is where the rewards begins for using multiple coils, higher output energies and hopefully efficiency.

Multiple Coil Design
     As the number of coils increase, so does overall size, weight and expense.  Not so much as the price of wire, which is negligible, but more so the extra switching devices and necessary driving circuits.  So why bother introducing this complexity to the design of coilguns, to exhaust the excess current from non-fully discharged capacitors, and mutually inclusive, to attain a higher ratio of Joules transfer from the source to the business end.  In other words, try to get more bang for the buck. 

Portable Coil Design
     Here is where benchtop single or multiple coil designs graduate into a battery powered hand held version.  Besides the usual electronics juggling between efficiency, components, and parts availablility and cost, a large portion of these designs, that I do not display here, is trying to design faster charging systems.  This becomes more crucial as the source energy increases with each model.

Rapid Fire Coil Design