The hold open device is the silver bar in the middle of the photo. When the magazine is inserted and latched or the last round is fired, the bullet follower on the mag pushes the device up and blocks the toggle in the open position.
Oops, I mean the bar that is sitting crosswise, not the safety.
So, does your Luger look like this one?
BTW, I lived in South Austin for many years in the Barton Heights area, great town!
