Steven,
The Luger firing pin engages the sear bar in about the last 1/4 inch of travel, so if the fired case is ejected length of travel is definitely not the problem.
The first thing that you should be aware of is that a firing pin which does not **** on breechblock return leaves the firing pin tip outside the face of the breechblock, which can lead to slam-fire and full-auto function.
The fact that this has not occurred may be diagnostic.
Does it consistently **** when you operate the action by hand? When the second shot fails to fire, can you re-**** it by hand?
With an empty chamber, observe the action of the sear bar as you pull the trigger. Does it move freely in the receiver extension, or does the sear spring return it to its rest position slowly or not at all?
The first action I would suggest is to remove the firing pin and thoroughly clean the firing pin cavityin the breechblock; the firing pin itself; the firing pin interior; and the firing pin spring and retainer. Examine the firing pin to see if the pin tip might be broken. When you reassemble it make sure that the firing pin moves freely inside the breechblock.
Remove the sear bar from the receiver extension and clean the receiver cut where it resides; the sear bar itself; and the disconnector plunger and spring. Check for free movement.
After you have done these things, take the gun out and shoot it. If the problem persists there may be other things to consider.
Do all the numbers on this Luger match, or is this a parts gun? More particularly, do the numbers of the breechblock, firing pin, sear bar, and receiver all match? If not, this in itself could lead to problems.
Sam is correcting in suggesting parts replacement; if parts are mismatched, or if they are worn, there is nothing lost by the attempt and it might solve the problem.
I'd suggest great caution before making the decision to file parts--the odds are in favor of your causing yourself more problems than less.
--Dwight
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