Try the P38 forum.
Yes.
9mm luger.
P38
Zero. Ruger never made the P38.
p38forum.com; the library, the internet.
Colt has never made a 9mm ruger combat commander
Of course! It's 9x19mm or 9mm Parabellum. The German Luger also used the 9x19mm.
Which one?
Contact Ruger Customer Service through their website.
You can request a manual for free at Ruger's web site.
ruger