Well, here's another piece of creative fiction!

[Vincent]

Thing is, the M1 rifle had the gas port at the muzzle too. I know, that's apples and oranges...

The FN49 gas port is relatively near the muzzle too. Maybe still apples and oranges, but a lot of the FAL gas system comes from the 49.

I would guess that shortening the barrel wastes a fair bit of the 7.62x51 cartridge propellant. Something like 7.62x39 would be better suited for the shorter barrel.