Hi Bill, it could certainly be dragging on the breechblock underside... but, try this first....Best if you can try another Luger as well... Field strip the luger, remove the firing pin, spring and retainer... Load the drum up with 25 rounds and cycle them thru by hand at the bench or range certainly while keeping the muzzle pointed in a safe direction... I use dummy rounds, and totally recommend only dummy rounds! But with care, you can find the issue using actual loaded rounds... AGAIN! It is then/now a loaded gun, and even with the firing pin removed, anything can happen!!!! Super careful with no one around!!! It should work at the bench just as well as shooting it... If you want me to send test dummy rounds to you, I will do so … Let me know, standing by... best to you, til...lat'r….GT
BTW, the problem may be the drum is too low, or too high in the Luger, one jams the bullet on the feed ramp (low), one drags on the feedlips(high)... but the fact that a bullet is always there means the drum is advancing correctly, just dragging some where?... Also, with the drum unloaded, push the follower down about an inch, so the hold open doesn't engage, and cycle the toggle several times to see if you can feel and drag when empty?
standing by!
BTW, it could still be the hold open in that the reinforcing fold on the right hand side of the mag tube at the top, can just touch the back of the hold open tab and it will just barely engage... a little Dremel action will clean it up... on either drum or hold open?...