I wonder if this would work energy-wise. A single cartridge of .38 Special—a fairly typical revolver round—can give a projectile around 350J of kinetic energy.

I wonder if this would work energy-wise. A single cartridge of .38 Special—a fairly typical revolver round—can give a projectile around 350J of kinetic energy. 9mm Luger is around 475J. A small rifle round like 5.56x45mm can give a projectile around 1750J of kinetic energy. This is just a fraction of the total energy, which comes out as recoil, operating the gun itself, and lots of heat. So the total chemical energy is probably at least double that. Now, you don’t if want to actually propel projectiles, you can go back to saving half of the energy again, but that just gets us back to the original number. Now let’s assume you’re going to replace the ammunition source with a battery. Batteries are slow to charge and guns are designed to have replaceable magazines so this would work for most gun types. A six round revolver cylinder would need about 2100J while a standard 15 round Glock 19 magazine would need about 7125J and a standard 30 round AR-15 magazine would need 52,500J. An iPhone 14 battery stores about 12.68 Watt-hours, which is over 45,000J. So far, so good. But you still wouldn’t be able to eject brass (because the brass would need to go where the battery goes), and you’d need some sort of electric piston to sit in the chamber and produce the “recoil”. Of course, this still wouldn’t prevent someone from loading a real magazine or cylinder with live rounds, which means this wouldn’t have prevented this incident.