The .300blackout was designed because the .223 just did not have the stopping power. This is a serious load. Problem right now is availability of the cartridge. Cabella’s, etc carry a variety of .223, etc but little in the .300 blackout. I get mine from a local gunshop. Bit more pricy than the .223 but it is a much stronger load, even in sub-sonic.
“The .300blackout was designed because the .223 just did not have the stopping power.”
No, the .300BLK was designed because the .223 does not function at subsonic velocities - and because AAC is first and foremost a suppressor manufacturer.
The .300 Whisper is close to fulfilling the intent of slapping a suppressor on an AR platform, but being a “wildcat” cartridge is designed and produced with insufficient rigor to make it as a viable military/CQB round. Refining the .300 Whisper for registering SAMMI specs, optimization for feeding in an AR platform with minimal adjustments (barrel & bolt, no change to magazine), and ensuring a hefty & reliable thumping at both supersonic and subsonic velocities at meaningful ranges, all emerged as the .300BLK design.
Having built the ammunition for impressive performance with a suppressor, AAC is now expanding platforms and accessories to make it a very attractive caliber - and make sales of accompanying suppressors a given. The AR platform was the first obvious choice, promoted with specialized uppers, whole guns, and culminating in their impressive “Honey Badger” gun. Being a serious caliber, and AAC having been purchased by Remington, the next obvious platform was a bolt action rifle, resulting in the Remington 700 AAC in .300BLK (pre-threaded for suppressor, of course). If you’re going to spend some $800 on a specialty rifle and a $1000 can to go with it, you’ll be wanting a suitable scope to mount thereon - hence the Nikon glass leading this thread.