You need X amount of gas at Y max pressure to accelerate a bullet to 1,050 fps or thereabouts. This is why .300 AAC BLK subsonic loads are typically around 220gr. If you go much lighter you need less gas to get the bullet to 1,050 fps and then you don't have enough gas to operate the bolt. If you increase the size of the gas port you can get around this problem to some extent. I went the .450 BM route and plan on shooting subsonic loads but with bullet weights in the 250gr to 300gr range there should be plenty of gas to work the action whether suppressed or not without the need for an adjustable gas block.
Spoke to the AR "guru" @ Wilson Combat today ( also, JP & Daniel Defense )...
...Wilson does NOT use an adjustable gas block for their .300AAC and their rifles cycle ALL ammo, unsurpassed flawlessly , sub to super.
In fact, he said he owns one with 16" barrel, ( I like the 14.7' "pinned" ) and no problem with subsonic without a "can".
The problems, he said, lie more with the variances in ammo manufacture and powders used. Some work well, others do not...find the ones that do and you are good to go.
He said they make their guns in such a way they shoot everything.
I believe him...if you ever dealt with Bill Wilson & Wilson Combat, you know what i'm talking about. Class act & company, amazing 1911 pistols and now the AR15 & 10's.
Now their .458SOCOM does use a adjustable block...and beefy buffer spring...but even when not, the power of the .458 seems to cycle reliably without, they do it because it is a great "hand-loaders" round.
It will inspire & motivate me to start reloading & hand-loaders too.