My new 300BLK SBR features a Faxon 8.5" CL 4150 1/8 with a gas port measured at 0.081", per Faxon. Gas Block is a pinned Geissele SGB done professionally by Rainier Arms LLC.

I'm running a Toolcraft C158 BCG, Tubb's LW Flatwire spring (lower pressure version), and inter-switched with an H/H2 buffer. The rifle cycles 123-125gr supers fine but 200-220gr subs will fire and eject but won't cycle. I tried fresh pmags as well. I didn't try a carbine buffer yet. The rifle would seldom lock back on the last subsonic round (only when 1 round is loaded in the mag)

I do have an AAC SDN6 still pending so I will fire subs suppressed BUT since I do like a variety of shooting any 300BLK rounds whether super/subs without a can reliably. Is it worth opening the gas port to .100 or .104? Would having a port this large cause any further issues when it is suppressed? I'm thinking excessive gas blowback.


Specs:

UPPER:
*Rainier Arms Milspec Forged Upper
*Faxon 8.5” 300BLK 5R Chrome-lined Barrel 4150 1/8 Twist (Rainier Arms Medium Contour) (.081" Gas Port)
*AAC BLACKOUT 51T 7.62 Muzzle Brake
*AAC 7.62 SDN-6 Suppressor (F4 Pending)
*Geissele Super Gas Block (Pinned)
*Toolcraft 1B1B6 C158 Phosphate BCG
*Geissele Super Modular Rail MK4 7” DDC
*Daniel Defense Fixed Sights Front/Rear
*Geissele Airborne Charging Handle DDC
*Geissele Super Precision MRO Lower 1/3 Mount DDC
*Trijicon MRO (Post 89000 SER.)
*SureFire M300C Scout Tan + UE07 Tape Switch
*Cloud Defensive Light Control System Mount MK1 FDE

LOWER:
*Rainier Arms Forged Lower
*LaRue Tactical MBT-2S Trigger
*Geissele LPK
*Geissele Maritime Bolt Catch
*Magpul Enhanced Aluminum Trigger Guard
*Griffin Armament Ambidextrous Safety Selector
*Magpul MOE+ Grip
*LWRCI Compact Stock
*LWRCI H2 Buffer
*BCM 7075-T6 Milspec Receiver Extension
*Tubb’s Lightweight SS Flatwire Buffer Spring (300BLK/Low Pressure Spring)
*BCM QD Endplate
*CrossTac 1-2 Point Sling Coyote Brown