Suppressed SBR Cycling Issue

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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Suppressed SBR Cycling Issue

Post by dward0487 »

I have a 300 BLK SBR that I built to run with a suppressor. The setup includes a BA 8.3" Hanson barrel (pistol length gas), the pinned BA low-pro gas block, a Lantac E-BCG, and the JP SCS (regular, non-heavy). I built it to be run suppressed with subs, with a Dead Air Nomad-30, including the E-Brake attachment.

I went to the range to test it out with Hornady BLACK (208gr A-MAX) subs, and while I was super happy with how whisper-quiet it was and how well it handled, the cycling reliability was dismal. Every 1-4 rounds, I would either encounter a failure to feed or experience a "click" because the bolt had closed on an empty chamber. The failures to feed always occurred with the bolt digging into the top of the brass case and hanging it up halfway into the chamber ("bolt over base" malfunction). I never encountered a failure to eject or a double-feed. The bolt also failed to lock back on an empty mag throughout the entire course of testing. I put 60 rounds through it before calling it a day.

So I've got a wide-open non-adjustable gas block, properly positioned (I use a Gas Block Genie when installing gas blocks) and secured with both the roll pin and set screws, and I'm running the lightest (all stainless steel weights) version of the Silent Captured Spring, and I've still got under-gassing issues... I did, however, have the stock black (85) spring installed in the SCS during testing instead of the lightest white (80) spring. Unfortunately, I had forgotten to bring my extra springs, so I didn't have a chance to switch out to the lighter one that day. I'll be testing things out soon with the white spring, and I'm hoping that will do the trick since my setup seems to be right on the edge of functioning reliably as it is. My concern, though, is what I'm going to do if that's still not enough to get the bolt to cycle and lock back consistently... I'm assuming the only option left at that point would be to send the barrel back to BA and have them enlarge the gas port.
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Re: Suppressed SBR Cycling Issue

Post by dpete »

What size is your gas port in the barrel? (measure it, DO NOT believe what any manufacturer says it is) Using numbered drill bits will get you close enough. I'de bet dollars to donuts your port size is too small. My 8" barreled SBR with the suppressor needed the port drilled out before it would run consistantly. Its at .108 right now but I can turn down the gas as I wish with the adjustable gas block.
The SCS may not be helping things either. I'm running a standard carbine spring and buffer. Don't complicate shiit with complicated shiit.
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