Several years ago I attempted to build a coil gun, but gave up in frustration after burning out several SCR's when designing the trigger circuit. The SCR is used as the switch that dumps the energy stored in the capacitor into the coil.
I've since brushed up on my fundamentals and tackled the problem once more. Below is the circuit I've come up with.
V2 applies a 3.3V, 10ms pulse to the gate of M1. This pulls the gate of M2 low and causes current to flow into the gate of the SCR. Since V2 is a logic-level signal, I used this configuration so I could drive M2 without needing a level-shifter. R1
R3 is a current limiting resistor used to limit the gate drive current to 40mA, which is the rated maximum gate current required to turn on the SCR.
R4 is used as a pull-down resistor to prevent spurious signals from triggering the gate of the SCR.
Since C1 is charged to 200V, I've included D1 to prevent the drain of M2 from seeing large voltages when the SCR is triggered.
L1 is the coil and D2 is used as a flyback diode to prevent reverse charging of C1.
I know I've left out some details, but is the overall design of this circuit good practices?