If you enjoy working up loads, it can get very expensive, but enjoyable.
For 150 grain supers, Shooters World Blackout or 1680. The Shooters World seems to be like a hot lot of 1680. You can get just a bit more powder in the same area, and it’s a bit faster. I’d buy whichever is available and cheaper to the door.
Shooters World Socom is right there with these two for performance.
N120, works well, is probably the cleanest of the bunch, but the slowest.
There are plenty of faster powders, slow pistol, that will work that will get you higher velocity, 296, Lilgun, 4227, Accurate 11fs. But I’ve never been able to get the consistent sub MOA accuracy that the fast fire powders deliver across radical temperature changes. My winter to summer temp swings can be over 100*.
The slower rifle powders like CFE and Lt 30, 4198 can be very accurate, but lose about 10% velocity. Depending on the bullet choice if hunting, that can mean the difference in effective range of well over 100 yards. Say the difference between 1900 and 2200 at the muzzle in a 16” barrel.
Be careful of the 150-55 grain bullets, as many will jam at magazine length. Even some of the 150 FMJ’s
16” barrel with carbine gas and buffer, unless a custom barrel with an “undersize” gas port, an adjustable gas block can be a very soft shooting rifle.
Off the shelf barrels will be ported to cycle subs, and crap off the shelf ammo. Not uncommon to see ports drilled to .125”. You just don’t need that much gas, for just supers you can get buy with .080” or less. My 16” is ported at .097”. Still shoot 175 grain subs without a suppressor and dial it way back with supers with an adjustable block. Don’t believe people that say you can’t over gas a Blackout. If it will cycle subs, it’s over gassed for supers by default. Yes, you can hyper cycle to a point where the bolt moves so fast the magazine can’t feed fast enough.
If you can get your hands on the Speer 150 gold dot, it’s probably my favorite. There are two versions, one specifically for 300 BLK, and one for 308.