What sort of tests would *you* want done on the alledged factory .45 Luger Carbine?
How would you attempt to prove or disprove it's authenticity?
(Bearing in mind the genius of some restorers, gunsmiths, and refinishers...)

I'd x-ray it. I'd magnuflux it.  I'd use dye penetrant.  I'd just take a really close look at it (like an electron microscope).  No matter what, there's a way to tell if a frame's been "widened" to handle .45ACP.

It's quite possible that the frame of the gun is completely custom made.  Basically then, you'd have to just examine the entire gun for any processes that couldn't have been made in the time period the carbine was supposed to be made.  If someone used a tool or device that couldn't have been around then, then that's pretty solid proof.  

Other than that, you'd have to find some antecdotal evidence that the thing actually existed in the first place to prove it's not an outright fake.

Ross

I quite agree Ross, the best proof would have to be in the provenance, (history).

If the gun was made with tools available to the era, (not unthinkable, where a million dollar price tag is involved,) finding *some* mention of it somewhere would be a small comfort.

If it was fabricated from scratch, and done with period correct tooling and finishes, there would be no Carbon 14 type dating that would apply, as it would not be organic material.

X rays and magnafluxing would only show a frame modification, not a completely new build.
Without provenance, it falls into the category of "extremely suspicious".

It is no higher standard that I hold this alleged .45 carbine to, than the
world would hold any as-yet-unheard-of other historic, artistic, or
genealogical treasure.

It is quite equivalent to some art dealer claiming to have found an
undiscovered DaVinci miniature baseball card sized painting of the Mona
Lisa. Most experts, rightfully, would say "Hogwash, prove it!"

It is equivalent to the old senile woman who claimed to be the lost Russian
princess Anastasia, who was debunked by genetic tests.

It is also equivalent to the "Hitler Diaries", that were greeted with
skepticism, auctioned for a ridiculous sum at Sotheby's, and also proven to be faked.

Without a solid line of provenance, we all know how age and metallurgy can
be faked. And the fact that not ONCE was this gun ever mentioned in any
records is a bit far fetched also.

This logic is not "guilty until proven innocent", this is good healthy
skepticism of outlandish and unlikely claims.
To act otherwise in the world of collectibles would be gullible.

The burden of proof lies with the seller.

I would have to Proof it at the range. If it can preform to expected levels, say a week or two of fun shooting, then I will be happy to swear that it's probably the real thing.

Even a fake, well done, would still have some value, that amount would be wide open, but WAY lower. If authenticity cannot be proven, it still remains a novelty, at least. To test it would mean having it in your sight and someone having to pay for extensive testing. And that may or may not confirm any conclusion. In any event, I would pass, leaving it to someone with more green matter than grey matter.

Good point, anothergene.
A modern made .45 cal Luger Carbine would have an approximate price tag of $25,000, I have heard.
A far cry from a million, but still quite a bit.
It is just frightening to see the lengths forgers have gone to, to fool people these days, though.
Not to mention the quality of their work!
Superb! Almost indistinguishable!
I wonder how many forgeries sit in museums and private collections already?
The modern ethical gunsmith fabricators and restorers are very careful to mark their work, so no none can later claim it as an original factory piece.
Again, without some original provenance, this gun is going to be a toughie to sell, even if it IS real.
Of course, some folks believe in the Easter Bunny too.

Hannah,  I suspect the first place to look closely is at the magazine.  The magazine should probably be the soft sheetmetal of the prewar lugers with the folded over seams.  That tooling could be a little tricky and you should see an appropriate accumulation of oxidation and/or lubricating crud in the side seams. Also I believe that pre WWI steel should be open pot Bessemer process (I think)  Anyhow is is not a process used today or even since the late 40's in the states.  Carbon content and distribution is different and this sometimes shows under very high magnification in the "grain" of the steel.  Regular microscope will do the trick.  I think  a binocular microscope of about 15X would do for look at the magazine for proper stretch and stress marks of and imperial era bending.  

Thank you Heinz!
I had forgotten about the Bessemer process.
This would indeed be a logical place to start and might shed some light.
I wonder if a small scale open top Bessemer can be duplicated in a mettalurgy lab though?
The corrosion and crud of the ages can easily enough be reproduced, I fear, but I think you are right about the different crystalline structure of the steel itself.
Excellent reply!
And welcome to the board!