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Posted: 9/1/2025 1:16:16 PM EDT
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So Iāve got an old QC10 9mm SBR, 4.5ā barrel with a 3-lug mounted Tirant. The triad 3-lug mount has been rockset to the can tubeā¦ slight but normal rotational play, but not wobble. That said, I dusted this thing off after several years - hadnāt shot it much since I had it cerakoated years ago, I think the smith dissasembled it when he did. I went out today to zero it with an MRO / 3x mag / bipod combo at 19 yards, after 2 mags when it heated up it was shooting minute of pie plate. What the hell? Can was solid, so are the optic mounts (Scalarworks). Any ideas whatās going on? I can say itās not me, because shortly after the groups pictured below I zeroed an AR at 25 yards and printed thoseā¦ and the same ammo shoots perfectly tight out of my pistols (147gr) Attached File Attached File Attached File Attached File Attached File |
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1st...verify the barrel nut is tight. If it's loose, there is your issue. 2nd...I would verify with other ammo. Try a mix of known quality factory 115, 124, and then 147 and see if you have the same grouping issues. If you see the groups shrink with 115/124, you may have a subsonic ammo issue. 3rd....if the suppressor can be removed, remove it and try the 115, 124, 147 test again. If you see the groups shrink, you might have a suppressor over-gas or mount issue. There may be back pressure and gas issues depending on how much is being captured in the suppressor. Weigh the current buffer and see what it is.....you may need to go 2-3 oz heavier to help slow down the bolt and give some more time for the ammo to burn longer. FWIW....on a 8in .22 build....I had good groups without the can. With the direct threaded can attached, the groups opened up a lot. But with a 16" barrel....the suppressor group stayed tight. Only thing I could come with was excess gas in the suppressor on the shorter barrel. AI answer is pretty much inline with my thoughts.... In a suppressed pistol-caliber carbine (PCC) with a short barrel, excess gas and increased back pressure can cause a range of issues, most notably larger groups on target. The primary cause is the destabilization of the bullet as it exits the barrel and travels through the suppressor. How excess gas affects accuracy Increased turbulence at the muzzle: With a shorter barrel, there is less time for the propellant gases to burn, resulting in more pressure at the muzzle when the bullet exits. The suppressor's baffles trap this gas, creating back pressure and turbulence. This disturbed, high-pressure gas can interfere with the bullet's flight path as it exits the crown of the barrel and travels down the suppressor's bore. Destabilization from unbalanced pressure: The bullet is designed to travel through a quiet, stable atmosphere. When it exits into a suppressor full of high-pressure, swirling gas, it can be nudged off its perfectly straight trajectory. This tiny deviation is compounded over distance, resulting in a larger group downrange. Solutions for better accuracy with a suppressed PCC Heavier buffer and spring: For blowback-operated PCCs, installing a heavier buffer and/or a stiffer spring is often the easiest and most cost-effective fix. This slows down the bolt's rearward travel, helping to tune the action for reliable and smoother operation with the increased back pressure. Different suppressor design: Suppressors with a flow-through or low-back-pressure design are engineered to mitigate this exact problem. By redirecting the gas forward, they reduce the turbulence at the muzzle and inside the suppressor, resulting in better accuracy, less recoil, and less gas in the face. Tuning the ammunition: Different ammunition loads have different propellant burn rates and produce varying amounts of gas. Experimenting with different ammunition, particularly those designed for suppressed shooting or with a lower powder charge, can improve accuracy. Delayed blowback systems: Some PCC platforms use a roller-delayed or other delayed blowback system. This design is highly effective at keeping gas in the system and away from the shooter and is known for shooting exceptionally well when suppressed. Different suppressor mounting methods: Using a different mount, such as one with a brake that is vented differently, can sometimes help redirect gas away from the bore and mitigate some of the turbulence |
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Originally Posted By HHjr: My 20+ yr old 6450 Does Not shoot 147ās accurately at All! Ā 115&124āsš Dude...the OP hasn't responded in 6 weeks. I don't think he's reading the responses or coming back. He's what I call a 1 post ghost....and boy are they common. They start a thread with the one post, and then disappear. . |
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