If I recall correctly, switch straight up it fed from both mag tubes alternating.That was always my impression of them. I lost all interest when i learned you have to flip a switch to use the other tube.
Switch left if only fed from left mag tube, switch right it fed from right mag tube, that way you could load buck in one side and slugs in the other for your choice.
Didn't make a damn where that switch was, it fucking jambed up.
I never got it to shoot the 14 rounds it held without an issue