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Posted: 7/12/2026 9:06:39 PM EDT
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7.5 psa upper. No name bcg. Only running subs. Winchester 200 gr. Rugged obsidian 9 suppressor. Pistol brace buffer tube. Ejecting fine at 4 o’clock but won’t pick up the next round. I’ve already opened the gas port to .125. I’ve tied 3 and 2.5 oz buffers. Even cut down the spring a few coils. What should I try next? Lighter buffer? Springco lighter spring? Open the port up more? Attached File Cut spring: Attached File |
"Government is like a baby. An alimentary canal with a big appetite at one end and no sense of responsibility at the other."
Ronald Reagan
Ronald Reagan
| Something sounds wrong. Are you properly lubed? Is there any binding? Are you sure it isnt somwthing stupid like your hand overriding the bolt catch? Is the bolt velocity too high such that its outrunning the catch? I run an H3, standard spring, and whatever a factory gas port size is on a Seekins 8.3" barrel and it runs super consistent in all four configs (super/subs/suppressed/non). You either have binding or that ammo is woefully underpowered because a setup with that lightweight of a recoil system will foul extremely quickly due to the insanely fast unlock of a setup that light. If it runs clean it will stop running reliably within a few mags, so be weary of that. |
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Are you running lancer mags? I see where you opened up the gas port to 0.125”, what happens with no can? No eject? 0.125” is likely way too much gas for 300 blkout Couple things I would try, pull a carrier out of another AR that runs well and test it, maybe that bcg has a gas leak. Any chance you have misalignment on your gas block? |
| On a totally different setup I had a similar problem. I tried everything over several months. Eventually I figured out the gas tube port hole had been drilled out of time with the roll pin hole. It wouldn't have mattered what I did, there was simply no way enough gas could get to the BCG. Replaced the gas tube and all the parts I fiddled with in the process. Everything ran proper with a properly made gas tube. |
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Originally Posted By -Obsessed-: Something sounds wrong. Are you properly lubed? Is there any binding? Are you sure it isnt somwthing stupid like your hand overriding the bolt catch? Is the bolt velocity too high such that its outrunning the catch? I run an H3, standard spring, and whatever a factory gas port size is on a Seekins 8.3" barrel and it runs super consistent in all four configs (super/subs/suppressed/non). You either have binding or that ammo is woefully underpowered because a setup with that lightweight of a recoil system will foul extremely quickly due to the insanely fast unlock of a setup that light. If it runs clean it will stop running reliably within a few mags, so be weary of that. Turns out it was the cheap bcg. Swapped in a higher quality one and now I’m 100%. Thx Attached File |
"Government is like a baby. An alimentary canal with a big appetite at one end and no sense of responsibility at the other."
Ronald Reagan
Ronald Reagan
| 99.99% of my 300 blackout tuning issues have been resolved by sticking with a carbine or h1 buffer, standard spring, and most importantly a known quality BCG. I have two setups that run barrels most internet experts say are traditionally undergassed. Both originally had no name nitrided house brand BCG's. Nothing wrong with these BCGs in a 5.56 gun. But with 300BLK subs they would not lock back on the last round. I swapped them out with a chrome lined phosphate microbest BCG (known for being very gas efficient) and an AO precision milspec and both setups now run like sewing machines. Supers. Subs. Suppressed and unsuppressed. No adjustable gas blocks. No drilling my gas ports. Not saying this will be the fix to your issue, but in lower pressure rounds like 300BLK a less than efficient BCG will occasionally cause you to chase your tail while trying to tune your gun. Plus IMO breaking out a drill and permanently altering your barrel should always be the last resort, not the first step, when tuning your guns...especially if the possible fix could be as simple as swapping the BCG, as you just found out. |
| You'll want to check the buffer face to see if its getting pitted from the BCG slamming into it. I had a KAK 7.62x39 7.5" barrel that came with a 1/8" port and had this happen. It only took one range session for it to occur. The recoil impulse was pretty harsh with the higher charged loads. Adding an adjustable gas block fixed the problem. |
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The pistol system in 300BLK AR's has low gas pressure to work with so you need an efficient action. Eliminate as much friction in all the moving parts as possible so that the energy from the gas tube goes into cycling the action rather than over coming friction. JP Enterprises precision 1-piece gas ring. Lantac Domed cam pin or PoF Roller Cam pin. BCG with sand cuts on bearing surfaces. Also, I have found that a Tubb LightWeight flat wire spring with an H2 or H3 buffer works much better than a standard strength spring with a lighter buffer. SpringCo Yellow spring is also good. And the best mags to use are MagPul 300BLK mags |
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Originally Posted By evnash: Turns out it was the cheap bcg. Swapped in a higher quality one and now I’m 100%. Thx https://www.ar15.com/media/mediaFiles/222048/IMG_0301_jpeg-3794756.JPG Test the other BCG for a gas leak. I had one leaking around the key that caused issues like you were seeing. Proper 5.56 ammo out of a 12.5” barrel with an OCL Polonium couldn’t even feed that BCG enough gas to be reliable lol. |
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