The secret to the Rem feeding the shorts was its, floating chamber. The barrel was bored out at the back to receive this chamber which was about the length of the short case. As it started to recoil the gas pressure hit the end of the chamber as well as the case & thus gave it more surface to push against so the impetus to eject the short. When a LR was fired the case extended beyond the chamber sealing the gap so it only received the thrust from the case head. Ingenious.& no doubt patented though I have never tried to look it up.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra