Bringing this old thread back from the dead.
The Federov was expensive and complicated to make, and prone to breakage in the field. For those reasons, not very many were made, and its service life was short.
The cartridge it used (6.5mm Jap) had almost 2000 foot-pounds at the muzzle, vs the M1 Carbine's almost 1000 foot-pounds at the muzzle.
The Federov weighed 11.4 pounds loaded. The M1 Carbine weighed 5.8 pounds loaded.
About 3,200 Federovs were made ... about 6.5 million M1 Carbines were made (plus civilian copies). A small number of Federovs were used in World War One - under 20, you read that right, under 20. Larger numbers of Federovs were used in the East Karelian Uprising and a thousand or so were used in the same area during World War II. Most Federovs were lost (presumed broken down and discarded) by the end of WWII. Millions of M1 Carbines were used in both Europe and the Pacific during World War II; it was in very widespread Marine Corps use by Iwo Jima and Okinawa. M1 Carbines were also heavily used in Korea and Vietnam. They were often supplied to foreign militaries after being decommissioned.
The Federov deserves credit as the first "assault rifle", or at least, has a claim. But saying that the M1 Carbine was just an updated or slightly tweaked version of the Federov makes no sense. The M1 Carbine is radically different from the Federov in purpose, size and weight, cartridge and service history. I am not aware of anything very much like the M1 Carbine, prior to the M1 Carbine.
Federov vs StG44 is a better comparison, since both weapons are more interesting as precursors than in terms of their own service history. I like historic weapons, but if I simply wanted an effective weapon to use in war, I would pick the AK-47 above the StG and the StG above the Federov. I would set the M1 Carbine to the side in that discussion, because it is not in the same category as those three, being much lighter and handier with a weaker round.
I will say this ... the Germans designing the StG44 apparently spent more time talking about the M1 Carbine than the Federov. I don't think they were copying the M1 Carbine by any means, they took it in a different direction (replacing Mausers, vs the M1 Carbine being intended to replace 1911s). But the M1 Carbine's effective use by U.S. troops and by partisan troops supplied by the U.S. got the Germans' attention and lent credence to the weapon designers who felt the Mauser was outdated.