Re: Suppressed Auto's
It's inaccurate on both counts, to my knowledge.
Now, in both cases, it's true that many people install adjustable gas systems for use with a silencer (a Schuster adjustable gas cylinder nut in the case of the M1A) to reduce the amount of gas driving the system, because the silencer increases back-pressure. But it isn't necessary.
The military's suppressed SR-25 and M-14 variants feature no gas system modifications.