My ACR will choke a couple shots when in "S" (yes, with a can mounted obviously
). And I've also seen others saying the same thing. It bleeds too much gas. I'd be interested to see what can they tested them with because mine is an M41K. If it were a .30 cal can I could maybe see the larger baffle area and internal volume eating up excess pressure but it's a pure 5.56 bore.
The smaller port on the "H/L" regulator I think is probably more of a fix for the current "U/S" regulator without having a confusing situation where the only way to differentiate which one you have is by measuring the port with a micrometer or pin gauge.
Without the benefit of having one on hand to test the theory I'm a little dubious as to if it will reliably cycle in the "H" position, with any spec ammo or without a can attached, if too much gas is bled off of the piston. We shall see. My plan is still to pick one up since it should solve the suppressed setting issue. What it's marked is immaterial I 'spose.