I was given the Luger Artillery model my "great uncle took off a German officer when the German surrendered" (as the family story goes).  Per the ATF letters it can be configured with a shoulder stock without going through NFA.

Now let me start by saying I'm not going to defile this heirloom, but if I put a new threaded barrel on it, can I still use the shoulder stock?  If my stock eligible pistol is damaged and the barrel replaced, is it still stock eligible?  The ATF letters don't say much about this and I know that "only" the artillery and navy models are eligible for the stock, but a suppressed luger with a shoulder stock seems pretty sexy to me.

You can affix a original or reproduction shoulder stock on the gun as long as it is an artillery type stock. Technically if it has the brass "Navy" stock it is not acceptable. As far as threading it and I mean no offense but you would be a monumental moron. Nice condition arties bring upwards of $3k without the stock you would be destroying it's value.

Absolutely agree with you about being a moran (spell it right, this is AR15.com after all).  I'm just wondering if replacing the barrel would make it illegal to use with a shoulder stock?

It's my understanding that if you modify a C&R firearm from it's original configuration, it losses it's C&R classification.
I think that would be the case if you threaded the original barrel or installed a new threaded one.

OP, whereas it is YOUR gun,

The item in question has very real value.  It is a moderately rare and highly collect-able Luger pistol.  Considering the money being discussed, you could purchase a nice little 9mm carbine and suppress it cheaper than ruining the value of a genuine Luger Artillery.

It you change the general configuration, you'll have to SBR it in addition to a suppressor stamp.

You can change out the barrel to an identical replacement and still use the shoulder stock but as mentioned, it has to be an identical replacement.  It can't be an inch longer to allow for threads, it can't be shorter than original, the sight has to be in the same place, it has to look original, etc.

Also, the Luger design is not the most durable action out there.  The added weight of a suppressor during recoil will add wear and tear to the toggle and bolt stop.  Potentially ruining a very nice pistol.

As others in this thread have said, please don't do it.  If you desire a suppressed carbine, just go buy one.

MLG

That's the information I was looking for and I finally found an answer on the ATF website to support it.

MLG, I was never really considering doing it to this pistol, just wondering if it could be done.