OK, I took some Q&D measurements...The Luger receiver is .941" minor dia; the Nambu is .858"; the Luger barrel thread is .714" OD...That leaves a .113" wall on the Luger receiver, and if you were to tap the Nambu receiver to Luger barrel thread size you'd get a .072" wall...That's kind of thin, I think...
The Luger barrel/breechface is .628", I'd re-thread the Luger barrel (or make a new barrel) to 5/8" x 18 and saw/tap the Nambu receiver to the same thread...The Nambu has almost no feed ramp, so that wouldn't be a problem...
I'm thinking 7.65 cal...If you did 9mm and wanted a similar profile, you'd need to thin it down quite a bit...Like Ithacaartist did with his 120mm barrel...
An Artillery Nambu??? I dunno...
OK, tell you what...There was a Type 14 barrel on GB last week for $76 start; nobody bid on it...It's relisted;
I put in a bid today; if I win, I'll sacrifice it for a longer/different caliber barrel...
