300 BLK

[bodiebill]

What is the ideal gas port length for supersonic loads?
For subsonic load

[bandook]

Carbine for supersonic, pistol for sub

[FIREBALL_BRIAN]

Pistol for both

[FMJBT]

Depends largely on overall barrel length and gas port size. In general though, I'd opt for pistol length gas on anything less than 16" for both supersonic and subsonic. Once you go to 16" or longer, a carbine gas system should work fine with supersonic but pistol will probably still be best for subs.

[Sam .223]

I run pistol length on my 16inch and can shoot both super and subs without issue.

[bruss01]

My guess would be go with pistol and use an adjustable gas block to fine-tune the supers.

[ar15barrels]

My guess would be go with pistol and use an adjustable gas block to fine-tune the supers.

With a correct gas port diameter at the pistol position, you don't NEED to re-tune for supersonic loads.
The supersonic loads go so much faster that the dwell time is similar for subsonic and supersonic loads.

The subsonic loads have MUCH lower port pressure on a carbine gassed 300 barrel than the supersonic loads do.
The problem comes in carbine gassed barrels where there is not enough dwell time with the subsonic loads to get enough gas volume into the gas system before the bullet leaves the muzzle.
The supersonic loads run higher pressures so they cycle a carbine gas system just fine.