Couple held for selling pen guns via Facebook

I too have struggled over the size of the cartridge shown as used. It is most often 22LR which is small, low pressure, low recoil and rimmed, all useful attributes for a pen gun. It really does look like 9mm Luger which is high pressure (35,000PSI), twice the pressure of a 38 special round and rimless which creates some nasty but not insuperable problems in restraining and igniting the round. Rimmed cartridges make it that much simpler and more reliable. Providing reasonable steel is used, the round will get out the front if it goes off. However, the risk of primer gas leak or failure (at 35,000PSI) is likely high and hand/wrist is injury almost certain with or without leather gloves, from recoil, gas leak, probable bounce back of the bolt handle &/or metal particles. Methinks his reason for 9mm is he has a sure supply; Police, military or a Rouge militia armourer friend. Anyway, the police may have up to 1130+ postal addresses to follow down from the customer records they kept & perhaps look for Tech Institute troublemakers with hand injuries through the schools or hospital records. Most people who fire one of those things in 9mm, even for test purposes will only want to do it once!