[Drakker]

If it happens only the first time it means something happens when you cycle it manually. Are you sure you are pushing the slide as far back as it can go? Its very easy to lock the slide on the hammer when cycling it manually. The recoil spring needs to work a bit to gather enough speed to overcome the hammer. On a perfectly tuned setup this should not happen... But unfortunately this is airsoft. Cheaper pistols do it all the time. Try putting the original TM hammer assembly back in and see if it still happens. Then try the TM BBU and nozzle. Try to find out which upgrade part is causing the problem then focus on that.