I wasn't looking for a carbine, but this one caught my eye when I noticed it had the original flip-up rear sight, and no bayonet adapter on it. Then I saw the "IBM" marking. It even had the correct-but-ugly stamped-and-brazed trigger housing, and laminated beech stock.
IBM was the only manufacturer that preserved all the paperwork from the carbine program, so it's only through those documents that we know of the identity of all the small companies that made the smaller components that were used by all manufacturers of the carbine. The idea was the prime contractor had to make the barrel, bolt, and receiver, and everything else had to come from small shops, and spread around all the prime contractors, to insure that all the parts would work together. Except for the smallest pins and springs, every part had initials on it that identified the manufacturer.
The program worked so well, that within a year the government had carbines coming out its ears, and canceled all contracts except for Winchester and Inland.
I did not know that! I was aware that of the 10 mfgs only six made their own barrels.