Just to stir the pot, "everybody knows" that Remingtons had iron frames. So did Thompsons.
But I had a BRASS 1928 Thompson in my hands about a year ago. Made in Turkey.
Legend is that the South sacrificed its church-bells to make pistols. Bells are not Brass: it gives too harsh a note.
They are Bronze. Copper and Tin, not Copper and Zinc.
That frame is not Brass. I would suggest a metallurgical analysis of the metal itself, and of the age of the patina.
With the equipment available today, it can be done.
If those are fakes, they are the best ones I have ever come across.
The Raisin Pie still stands.