Suppressing an SBR vs 16" Carbine - gas blowback expectation

[masakari]

Two of my rifles are candidates for getting a suppressor, a SilencerCo Omega, when tax return comes. They are:

11.25" Colt 6940 (cut down) with .073 gas port and H3 buffer

16" Colt 6720 Carbine with Spike's ST-T2 buffer (I know that those buffers aren't liked around here, but that's not part of this discussion)

Am I right to assume that the 11.25" rifle will have more gas blowback than the 16"? Is that something that needs to be tested to see if it's even an issue?
I'm considering getting an AXTS Freedom Bone charging handle to test with the suppressor, debating on getting one or two for each rifle.
Thanks guys.

[MistWolf]

If it has a larger gas port, I'd say you're more likely to have gas to the face with the shorter barrel. If the gas port diameters are the same, I'd say the longer barrel is more likely to give you gas to the face as it will take longer to vent. Only way to tell if it's gonna be a problem is to go shoot them

[VelveteenMole]

I don't know the port size on a 6720, but I think a major factor in this is that the lack of dwell time between the port location and the muzzle of really short SBRs forces you to run the BCG at much higher pressure, faster, thus unlocking the bolt earlier relative to residual can pressure. Frankly I doubt a carbine gassed 16" won't be over-ported thus nulling the advantage I'm suggesting, but I think I'm right in theory assuming equally well tuned porting. It also might be a matter of compressability and inertia of the column of gas in the longer barrel letting more out of the front of the can.

I definitely get less crud in my 16" intermediate ported recce with an SLR adjustable gas block than in my 10.5" carbine ported SBR. Neither are notable for gas to the face though. There are so many variables involved with timing of events and pressures and component options it's possible that the answer isn't remotely reliable from one match-up to the next.