keep in mind the whole reason anyone might want a 300 black-out cartridge to use in a AR platform,
is to use it in a carbine with a suppressor, as that is its main reason for its being designed,
as the cartridge is designed to maximize the potential of the AR 15 platform with a suppressor,
the cartridge is designed to have all its potential velocity potential reached in a 10"-12" barrel ,
and reach perhaps 90% of that potential in an 8" barrel,
, .and with an added suppressor to keep the length of the carbine a under the length of a 18"-20" barrel ar15 rifle
to truly be successful in suppressor use the projectile must not exceed the speed of sound so you must load the heaviest possible projectile with the greatest sectional density to about 1000 fps max, and to maintain accuracy that will require about a 1 in 7 or 1 in 8" twist rate to stabilize a 200-220 grain 30 caliber projectile
I fully expect sales of the 300 BLK in AR15 kits to get far more popular
this 300 blk, is not a hunting cartridge or a battle rifle cartridge,
it can be loaded to nearly duplicate the 7.62/39 AK cartridge if used unsuppressed
its designed to be a big improvement over s 9mm pistol cartridge in a suppressed carbine
think of it as a sub machine gun cartridge, thats been designed for suppressor use,
to take out sentries or to be used where no muzzle flash or sonic crack is preferred/required


https://thebiggamehuntingblog.com/55...08-winchester/


300 black-out,
you might want to think of the 300 black-out as
a cartridge that was primarily designed for suppressor use

https://www.80-lower.com/products/3...-handguard-side-charged-w-80-lower-1-8-twist/
these plated cast, 220 grain, bullets are designed to use with a suppressor,
in a 300 black-out, cartridge in an AR15 carbine ,with a suppressor,
typically a 10"-16" barrel to keep the over all length reasonable.
they cost only about 20 cents each keep the velocity below 1150-1200 fps.
faster powders preferred, remember your limited to about 1000 fps max if you are to avoid the sonic crack of the bullet breaking the sound barrier, so pushing a 190grain-220 grain projectile greatly adds penetration, if thus limited in velocity, but a 30 caliber projectile weighting 220 grains requires a fast rifle twist for stabilization,
the 300 black-out , loaded with the 220 grain bullet,
has easily more than double the typical 9mm carbines power at 100 yards

https://hodgdon.com/wp-content/uploa...data-final.pdf
10.5 grains of IMR 4198
is a common well liked load in a suppressed 300 black-out with a 220 grain bullet

and use a 7:1-to-9:1 twist rate barrel to maximize accuracy and not have suppressor issues,
remember you want to have heavy and accurate projectiles leave the suppressor,
be below the sound barrier,
this 220 grain plated bullet in a 300 black out,
far exceeds the typical 9mm sub machine guns power ,
accuracy, range and penetration,
https://www.wideners.com/reloading-...-grain-plated-spire-point-500-bullets-reviews
with a 220 grain bullet at 1000 fps, making it far more lethal than a 9mm submachine gun cartridge,
at ranges out to about 150 yards with a suppressor in use,