Where to start - where to start?
Firstly, 5MF and I are friends. I've been a guest in his home. Having said that, even though his responses ARE 110% correct, his manner, and often flippant-sounding sarcasm, at times annoy even me. But, look past that - he HAS the facts!
I've been collecting longer, and published the first half of a guidebook on trapdoors, but he is doing REAL research on an unprecedented scale. His work, when published in about ten years, will DWARF Mallory and Brophy. He has already found much they missed. I'm not kidding.
Back to your carbine:
Is it real? Yes, mostly - the stock cannot be faked (but it well could have been swapped. Has the arm always been as we see it? NO. Who scrambled the parts? We'll never know. What does the "C" mean on the rifle sight leaf? Certainly NOT "carbine". Based on earlier arms, I THINK it means condemned - note the apparent damage at around the midpoint. What's it worth? What you can get for it. The receiver was issued to O'Neill - but the MANY incompatible finish and wear issues will degrade the price greatly. The bit about the stocks being installed immediately prior to shipment is, I believe, an "uncle Charlie" story, NOT based on fact. That certainly is not how the trapdoors were handled. Could it be a Bannerman? Yes.
Hope that helps. Please feel free to continue the discussion!