[Steinar]

I always check the shell of reloads with a caliper to see if it has been stretched. Believe it's worse if it's too long, leaving the bullet with too little free run.

In your case it seems as if it's just the bullet that is shorter by 1mm, that's not much.. as long as it's a round nose, I don't think that’s your problem. As you probably know, the Luger scrupulous about it's ammunition. Bullet weight or powder used is more likely the cause I believe.