I replaced the noveske switchblock on my 12.5 5.56 uppers. I don’t have to adjust it suppressed or not, but then again I don’t shoot subsonic anything through it obviously.

With such huge bullet weight range on the 300, is an adjustable gas block necessary?

It was for me. Have a 10” barrel and I use it with a can, so I set it up to work with those, and it cycles anything else with or w/o the can on it.

Definitely nice to have.

Required? Not in my experience. I have shot 125 and 150 gr supers, 190~220 gr subs, suppressed and non, without a hiccup. PSA upper

Nice but not mandatory for me. I have a 7.5” bbl .300 Blk but almost always run it suppressed. No issues with subs or supers but it can get a little gassy with the supers.

10.3" Wilson Combat 300blk upper here. Fixed gas block.

My first couple dozen rounds were unsuppressed, both supersonic and subsonic. No cycling issues.

Since then I've shot everything suppressed, mainly supersonic but some subsonic. No cycling issues.

Surefire SOCOM RC2 mini suppressor. No gassing issues.