Make sure the gun is unloaded and remove the magazine.
Remove the sideplate from your Luger, and then reassemble the upper to the lower receiver and close the takedown lever.
Now with the sideplace removed, pull the toggle
fully back and let it snap forward on its own inertia... Your pistol should now have the firing pin held back by the sear in the firing position.
You test this by applying pressure to the front of the sear in the same manner as the "L" shaped lever would apply pressure if the sideplate were attached. If you do this you should hear the unmistakeable CLICK of the firing pin dropping to the FIRED position.
If you can repeat this test, every time you pull the toggle fully back and let it go, and you can hear the firing pin drop, then the problem is not with the Luger, but with the sideplate.
If the firing pin does not drop for this test, even once, then the problem maybe partially, if not fully, with the parts installed on the upper receiver.
Please post the results of your testing here, and I will provide additional guidance based on your results.
