If your Luger is jamming then you need a full cleaning and tune-up. Check for a warping of the barrel which is common the 38's and Lugers alike.
personally I wouldn't be going out on the range or wherver you folks take part for target practice with a firearm in this condition. Since you have a visible recoil mechanism on the P-08 this could actually come apart and backfire in your face, not a very pretty sight. And secondly be very careful of WW 2 ammo as I have quite a bit of 9mm parabellum as it may have old powder and rust within, another cause for concern in mis-fires.
In fact I am looking at a small narrow cardboard box of 16 rounds marked Pisotlenpatronen 08 L.E. 1944 dou. 59
looks very clean but it stays in the box and will not be fired for the reasons described......if you guyz want to take the chance go ahead as now you have been warned ! keep the original box and rounds as part of your collection.....

~E