300 BLK vs 5.56mm for barrel length efficiency

[why1504]

With a focus on 300 Blackout:

What barrel length is best for sub sonic ammo?

Sub sonic Suppressed?

A mix of sub sonic and supersonic ammo suppressed and unsuppressed?

[Quiet Riot]

With a focus on 300 Blackout:

What barrel length is best for sub sonic ammo?

Sub sonic Suppressed?

A mix of sub sonic and supersonic ammo suppressed and unsuppressed?

Barrel length doesn't have the impact on subsonic ammo that it does on supersonic because you can load your rounds to be right at 1050fps regardless of the length you choose. Getting the action to cycle is then a matter of tuning your port size.

AAC sells a 9" barrel that is designed to cycle subs unsuppressed through supers suppressed. You could go shorter if, again, you tuned the port size to allow cycling subs unsuppressed.

The same question is always worth asking, though- why would you want to shoot any real quantity of expensive, underpowered subsonic ammo without a suppressor?

It's also worth noting that Noveske specifically tunes their 300 BLK barrels so that they DON'T usually cycle subs unsuppressed because they feel their port size makes supers suppressed more reliable. AAC might disagree, but I literally put my money on Noveske when I bought their 8" barrel.