Posted: 1/7/2026 11:01:27 PM EDT
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Hey all, Trying to troubleshoot a new build. I have a Criterion Hybrid Stainless Nitride with ops inc brake and collar. After troubleshooting, I have found that with an ops inc brake and collar, the gun shoots on average 0.75moa worse than without either installed. I believe this is mostly the brake and have a replacement and flash hider in order, but the collar I think is also a factor based on 2x groups I shot with the collar, no brake. The muzzle device was torqued to less than 30ft-lbs, so I'm sure it's not overtorquing that could cause this. Assuming I dont just have a bad brake that is kissing the rounds, what causes this sort of behavior from a muzzle device? When contacting criterion they started talking about barrel harmonics. How "real" is that, and is there any real solution other than trying different accessories and see if I can find a good combination? Thanks |
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Are you shooting factory ammo or your own handloads/reloads? I tried about a dozen different factory loads for my lightweight 11.5” BCM barrel with can until I found a load that grouped at about 1 MOA. Everything else I tried patterned at 3 MOA or worse. I was shocked how badly that barrel performs with so many different loads. For my 24” DPMS in 6.5 Creedmoor, it took me only five handloads at .2 grains difference per load to find a load that will do about .5 MOA if I’m on my game. |
Knight of Blunder - Fogo '21
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Barrel harmonics are very real. Anything that changes the mass of your barrel, especially at the muzzle end, will change its resonant frequency. When you fire, all that energy causes the barrel to resonate. Basically, the muzzle waves back-and-forth at a frequency determined by its length, mass, and points of contact with either the environment or other parts of the firearm. You can typically tune it out by handloading--when you find a really accurate load, you are generally finding a specific bullet acceleration/velocity profile that results in the bullet leaving the muzzle at minimum deflection, which makes it consistent from shot-to-shot. The other end of the spectrum is exiting the muzzle at max deflection. A barrel is not guaranteed to flex in the same direction with each shot, so the muzzle basically "flings" the bullet a bit in some random direction that's different with each shot, resulting in your groups opening up. |
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Originally Posted By Scott_S: Are you shooting factory ammo or your own handloads/reloads? I tried about a dozen different factory loads for my lightweight 11.5” BCM barrel with can until I found a load that grouped at about 1 MOA. Everything else I tried patterned at 3 MOA or worse. I was shocked how badly that barrel performs with so many different loads. For my 24” DPMS in 6.5 Creedmoor, it took me only five handloads at .2 grains difference per load to find a load that will do about .5 MOA if I’m on my game. Shooting factory ammo, 3x different grains of FGMM, AAC 75gr, Hornady Black 75 gr BTHP, among others. Same results on everything. My goal is not to get crazy accuracy, frankly all I'm trying to do is get under 2moa with affordable match ammo (AAC, Hornady Black, IMI if i find a sale, etc), but the 0.75 shift is putting me outside that goal. It sounds like savings for a reloading setup is in my future. |
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Originally Posted By 2ANut: Barrel harmonics are very real. Anything that changes the mass of your barrel, especially at the muzzle end, will change its resonant frequency. When you fire, all that energy causes the barrel to resonate. Basically, the muzzle waves back-and-forth at a frequency determined by its length, mass, and points of contact with either the environment or other parts of the firearm. You can typically tune it out by handloading--when you find a really accurate load, you are generally finding a specific bullet acceleration/velocity profile that results in the bullet leaving the muzzle at minimum deflection, which makes it consistent from shot-to-shot. The other end of the spectrum is exiting the muzzle at max deflection. A barrel is not guaranteed to flex in the same direction with each shot, so the muzzle basically "flings" the bullet a bit in some random direction that's different with each shot, resulting in your groups opening up. Thanks for the explanation. It sounds like a reloading setup is in my future, but in the meantime, i might just try different gas block and muzzle device combinations to see if I can tweak the harmonics. |
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While this is for a high end bolt gun here is an example of what differences different muzzle treatments does. This is a 6.5 Creedmoor with a barrel that tapers to .98” at the muzzle. First group=thread protector. Second group= Full Nelson can. Third and 4th groups = brake. Attached File The brake now lives on that gun. |
Joined:
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KY, USA
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What are you expecting out of the build? A true MOA gas gun is a rare bird, and usually made by JP, Seekins, GAP or someone like Craddock spinning up a Bartlein, Proof, or Kreiger blank. Some guys can get there with premium components at home, and taking their time. Five shot groups do not tell the tale of any system. That is mathematically proven. |
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When different people say "barrel harmonics" they mean different things. I don’t like the term because it's not well defined. Most things that reduce group size get discovered by trial and error, not from rigorous data collection and analysis. Many shooters often don't collect enough data to segregate signal from noise, including me. Putting different things on a muzzle can impact group size. Find what works for your barrel, and don't worry so much about why. As for why some bullet, powder, and charge combos work better than others, the chances that it's caused by stumbling upon a combination that exits the bullet from the muzzle at the time of the muzzle's minimal "harmonic" deviation from its resting point are so remote that they might as well be non-existent, in my opinion. For example, I have a 50 grain V-Max/Benchmark load and a 77 grain TMK/Varget load that work nearly optimally across a wide variety of AR barrel lengths and profiles. That should not happen according to the "harmonic" theory of reloading, yet broadly accurate bullet/powder type and charge combos are common. Sierra even publishes them for their bullets. |
