I did a quick search and stumbled upon a few threads mentioning what to do when suppressing an M1A, and the consensus is to use a Shuster adjustable gas plug to deal with the gas blowback.
I also saw a comment that the user Ted Brown was looking to create a new gas valve that required no modification to the plug but that was from 2016.
So far I have a scoped 22" M1A that I am thinking about getting a Shuster gas plug and Smith Enterprises threaded adapter for.
So anyway, I'm looking for what is new out there for suppressing an M14 and if anyone here has a setup that they'd share.