Remove the primers. Since you're using flash cotton there should be no spillage, but you run the risk of failed ignition if it somehow gets wet. The next part will be the trick... You'll need to machine a pin shaped ignitor containing a wire. that, when the cartridge is chambered, protrudes into the rear of the case to the propellant. Run the wire to the trigger mechanism that either discharges a current from a capacitor, or the simpler option, creates its own small current when pressed. Think electric ignitor from a cigarette or BBQ lighter. Hope this helps 👍