Adam,
To add to Dwight's excellent info., you luger seems to have received a 6' 9mm barrel somewhere along the line.
Original 6" barrels only came on the Navy luger, but many 1920's Weimar period lugers with shorter than 4" .30 cal. barrels get rebarreled, especially for USA shooters. That is why one-half of the barrel-receiver "witness mark" is missing on the barrel's shoulder where it screws into the receiver (which retains its original witness mark stamping...)
Looks like a very decent buy at $ 400 and a gun you can shoot without worry that a high-dollar collector-grade luger is at risk...
Have a local gunsmith check her out before you do any shooting...
Regards,
Pete... <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />