This is a picture from 1942 tests with the M1 Carbine. The tests performed at Aberdeen Proving Grounds were experimenting with different gas systems as shown.
Notice the lower carbine has a piston much like the M14. This was an early test of the "Gas Expansion Cut Off" principle which evidentually was used on all the T44 series, including the T44E4 and E5, (M14 and M15 HB)
Sometimes it is hard to believe that what we see today was actually being developed so long ago.