won't fire 6 cartridge
 

Had a full magazine of 9mm, first 5 cartridges fired, and
6th cartridge loaded into chamber, but pulling on trigger
did not fire. Problem with sear bar plunger (disconnector)
or bad magazine?
Ray

Since it chambered OK, I'd suspect the disconnect plunger. Seems to be in fashion this week!

Try soaking it in something that will free up any gunk that might be sticking the plunger in the front of the sear bar.

Also check and make sure the pistol has a tight square trigger plate fit and no looseness.

Is this a new problem, or have you fired it before/

I never fired this old 1917 military luger before. Who knows
if the gun has been fired in 20 years.

Then start with a field strip, thorough clean and lubrication.
Pay special attention to the plunger on the sear bar, it must move quite freely and it has a very light spring- so it is easily gummed up.