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Posted: 2/10/2025 9:45:53 AM EDT
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I have a CMMG SBR with a YHM free float handguard and an 11.5" barrel(5.56), and a F1 can (D cell 8") It shoots about 1 MOA without the can. When I use the can I cannot get a good group at all. When I put it on my 16" M4 profile PSA barrel it changes POI which I expect, but accuracy isn't affected. Is the CMMG barrel too short to hang a long can off of it and expect it to keep it's accuracy? I have inspected the baffles (freeze plugs) and there are not any baffle strikes. What is the shortest barrel I can put the can on and expect accuracy not to be affected? Thank you for any advice. |
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Originally Posted By bluedog82: Barrel length is not correlated to accuracy, as long as you have a sufficient twist rate. Have you tried this can on other barrels? No offense, but being an F1 can it may simply not be conducive to accuracy. When I put it on my 16" M4 profile PSA barrel it changes POI which I expect, but accuracy isn't affected. |
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I also have a 30 cal F1 can for my 7.62x39 AR and it does not affect accuracy. The can is the same design as the 5.56. the 30 cal can is on an 11.5" Bear Creek Arsenal 7.62x39 AR, I have also shot it on my 16" 7.62x39. Accuracy does not change, just POI. I put the 30 cal can on the 11.5" 5.56 SBR and accuracy is changed. |
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Originally Posted By joeIII223: I also have a 30 cal F1 can for my 7.62x39 AR and it does not affect accuracy. The can is the same design as the 5.56. the 30 cal can is on an 11.5" Bear Creek Arsenal 7.62x39 AR, I have also shot it on my 16" 7.62x39. Accuracy does not change, just POI. I put the 30 cal can on the 11.5" 5.56 SBR and accuracy is changed. What mount is on the 11.5? |
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If the 11.5" is producing erratic/random shot placement that's out of the ordinary for that rifle, and the 16" is shooting the same groups with or without it, it probably because of the 11.5" barrel and I will explain why, and what I've learned over a decade of building them. When you attach something to your barrel it changes several things, but a suppresor in particular will most drastically effect the atmosphere immediately around the projectile. If you have a slightly crooked, but perfectly concentric baffle it might create higher pressure at 12o'clock causing the bullet to drift slightly down. The next baffle might cause a drift towards 4o'clock, so now it's drifting down and right. If this pressure change isn't consistent from shot to shot, your groups begin to open up. I know the rule of thumb is that barrel length has little bearing on accuracy, but that's not always the case. An 11.5" barrel has a tremendous amount of unburned powder and excess gasses. These gases are traveling much faster than the bullet is. When they hit a baffle it causes substantial turbulence and pressure waves that the bullet has to travel through. If it begins to drift at all, it will continue to drift. Shorter barrels behind a suppressor that upsets the atmosphere too much will have less consistent groupings, than suppressors that dont. Then we have to consider the pressure generated by the gas colliding with that baffle. Shorter barrel, more uncorking pressure. Is the suppresor flexing? Is it causing the barrel to flex? Is the laminar flow behind the bullet causing it to start tilting? The first 2" out of the barrel the gas is traveling faster than the bullet. In free air a super sonic round will exceed the gas velocity right about 2" beyond the muzzle. In a suppressor, you create (on purpose) substantial turbulence for sound suppression, but it sucks for accuracy. The only answers I know of are use a better design or use a longer barrel. You could try a heavier bullet. Pressure drift diminishes as bullet weight goes up.A 62gr might do it for you. Anything above 90-100 grain, I've not been able to perceive it, but that's too heavy for 223/5.56 calibers |
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Originally Posted By shooter64738: If the 11.5" is producing erratic/random shot placement that's out of the ordinary for that rifle, and the 16" is shooting the same groups with or without it, it probably because of the 11.5" barrel and I will explain why, and what I've learned over a decade of building them. When you attach something to your barrel it changes several things, but a suppresor in particular will most drastically effect the atmosphere immediately around the projectile. If you have a slightly crooked, but perfectly concentric baffle it might create higher pressure at 12o'clock causing the bullet to drift slightly down. The next baffle might cause a drift towards 4o'clock, so now it's drifting down and right. If this pressure change isn't consistent from shot to shot, your groups begin to open up. I know the rule of thumb is that barrel length has little bearing on accuracy, but that's not always the case. An 11.5" barrel has a tremendous amount of unburned powder and excess gasses. These gases are traveling much faster than the bullet is. When they hit a baffle it causes substantial turbulence and pressure waves that the bullet has to travel through. If it begins to drift at all, it will continue to drift. Shorter barrels behind a suppressor that upsets the atmosphere too much will have less consistent groupings, than suppressors that dont. Then we have to consider the pressure generated by the gas colliding with that baffle. Shorter barrel, more uncorking pressure. Is the suppresor flexing? Is it causing the barrel to flex? Is the laminar flow behind the bullet causing it to start tilting? The first 2" out of the barrel the gas is traveling faster than the bullet. In free air a super sonic round will exceed the gas velocity right about 2" beyond the muzzle. In a suppressor, you create (on purpose) substantial turbulence for sound suppression, but it sucks for accuracy. The only answers I know of are use a better design or use a longer barrel. You could try a heavier bullet. Pressure drift diminishes as bullet weight goes up.A 62gr might do it for you. Anything above 90-100 grain, I've not been able to perceive it, but that's too heavy for 223/5.56 calibers Great explanation. What do you think the minimum barrel length I could get away with and still have an accurate group? Or should I just buy a F4 suppressor? Some of them claim no group change from suppressed to un-supprssed, possibly POI change (which isn't a big deal for me). |
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Everything you need to know about the left was on display during covid . -RC03
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Originally Posted By joeIII223: Great explanation. What do you think the minimum barrel length I could get away with and still have an accurate group? Or should I just buy a F4 suppressor? Some of them claim no group change from suppressed to un-supprssed, possibly POI change (which isn't a big deal for me). Well, I wanna clarify it could be something else, but if the 11.5 shoots 1" naked, and 5" suppressed that excess gas would be my primary suspicion. If it's 1" naked, and 1.5" suppressed, that could just be barrel harmonics. The very first change I made that I saw a noticed improvement on, was making the first baffle as tight as I could. For 22cal I went from .300 bore to .250, and even some .230 bore. First baffle placed 1.5 ahead of the muzzle. If a break was on the barrel, I used half it's length. If the break is 2" long, 1" counted another .5" gave me 1.5" from the muzzle (even though the baffle was only 0. 5" passed the muzzle break). I totaly made that up, but I didn't want the suppressors to be ridiculously long. The point being, I want the bullet out of the tornado of gasses before I started stripping gases. If it's to close it interferes on the primary gas path, if it's to far it interferes on the secondary (after it hits the baffle) path. From there it was pretty typical designs. What we settled on, is a helix blast chamber that's 2" long, and then baffles after. We only settled on this because it is the most repeatably accurate, and partly due to slowing the gas in a less direct way. Once the bullet is beyond that gas tornado, you can do what you want. We stopped clipping baffles on rimfire cans (which is mostly what we work in these days) because there was repeated difference in group sizes from target shooters. It was very small, but it was def there. So what's your bore size, and how far from the muzzle end is the blast baffle? Do you have a mount on it, or is direct thread on both barrels? |
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1 lb 4 oz Steel freeze plugs. I think there is a baffles strike in a few of them. The holes in the baffles are about .280 Blast chamber is made from the top of a chain link fence and is 2.660 long. Overall lenght of suppressor is 9". Bottom photo is the break it threads on to. If i were to mfg another F1 can I would probably turn the baffles on a lathe and make the holes larger. Thoughts? @shooter64738 Attached File Attached File Attached File Attached File Attached File |
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Originally Posted By bluedog82: With wait times being measured in hours or days now, it’s definitely a good time to get a F4 can, especially if you don’t have any. I am saving for one. There are so many different cans it's information overload. Been looking at these. Any opinions? https://www.silencershop.com/otter-creek-labs-polonium.html The CQB 556 on this page https://brm-silencers.com/products/#PRODUCTCQB |
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Originally Posted By joeIII223: I am saving for one. There are so many different cans it's information overload. Been looking at these. Any opinions? https://www.silencershop.com/otter-creek-labs-polonium.html The CQB 556 on this page https://brm-silencers.com/products/#PRODUCTCQB I have the shorter version, the Polonium K, and it’s an excellent value. The full size is great, too, just be aware that they are higher backpressure. I’ve never heard of that second company…there are plenty of great cans from well known manufacturers for that price.  Failed To Load Title |
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Originally Posted By bluedog82: I have the shorter version, the Polonium K, and it’s an excellent value. The full size is great, too, just be aware that they are higher backpressure. I’ve never heard of that second company…there are plenty of great cans from well known manufacturers for that price.  https://www.youtube.com/watch?v=jdzGB1AZrlQThanks I took a 2 gun class and the instructor had the BRM can and it sounded great. 3D printed titanium core. I'm doing my research and am considering the mfg in the video. I do like the price. |
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Wonder if tolerance stacking & the weight of the can is causing a baffle strike. That first photo definitely looks like it's had contact. Have you used an alignment rod to check? If it is, you could probably open the baffles up a little without loosing any noticeable suppression. Edit I would also be suspect of the SD brake, some of their stuff is inconsistent & loose tolerance wise. Bought a booster from them awhile back & the piston was way out of spec. They replaced it but it should of been caught earlier. |
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Originally Posted By Wangstang: When mounted, how far is your gass block from contacting the handguard? How about the distance of the can to the handguard? The gas block has clearance in the handguard, I haven't checked how much. From what I remember the can is far enough away from the handguard. I am at work and won't be able to check those until later this week. |
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Originally Posted By Asylum9: Wonder if tolerance stacking & the weight of the can is causing a baffle strike. That first photo definitely looks like it's had contact. Have you used an alignment rod to check? If it is, you could probably open the baffles up a little without loosing any noticeable suppression. Edit I would also be suspect of the SD brake, some of their stuff is inconsistent & loose tolerance wise. Bought a booster from them awhile back & the piston was way out of spec. They replaced it but it should of been caught earlier. I was thinking of opening up the baffles, don't have an alignment rod. That would be a cheap investment. Thanks |
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Originally Posted By joeIII223: I was thinking of opening up the baffles, don't have an alignment rod. That would be a cheap investment. Thanks I’d also recommend keeping Teflon tape away from the torque shoulder of the muzzle device. That can cock a mounting enough to get a front cap kiss / strike. |
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Originally Posted By joeIII223: I was thinking of opening up the baffles, don't have an alignment rod. That would be a cheap investment. Thanks Originally Posted By joeIII223: I was thinking of opening up the baffles, don't have an alignment rod. That would be a cheap investment. Thanks You don't need a rod. It's just like using iron sights. Looking down the barrel, you'll have "3 circles": the start of the rifling (just after the throat), the end of the rifling (the muzzle), and the distal cap (silencer exit). Center the muzzle exit circle inside the rifling start circle (rear sight and front sight alignment). Does the silencer exit circle look centered to these (target alignment)? If not, you don't have proper concentricity (this is what the rod would show you). Originally Posted By KalmanPhilter: I’d also recommend keeping Teflon tape away from the torque shoulder of the muzzle device. Absolutely. Also, is that a tapered interface? If so, teflon shouldn't be needed on the threads. Thread together until the tapered surfaces start to touch. With a firm hand on the rifle and the other on the silencer, twist the silencer CCW (loosening) ~1/4 turn, and (in one swift motion) twist back CW, firmly seating the taper interface. Make sure to use just a bit of anti-sieze on all threads (I recommend Loctite LB8009) and a drop of light oil on the taper face. |
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Originally Posted By KalmanPhilter: I’d also recommend keeping Teflon tape away from the torque shoulder of the muzzle device. That can cock a mounting enough to get a front cap kiss / strike. Break is not tapered. It will start to back off in less than 30 rounds without the tape. |
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Originally Posted By joeIII223: Break is not tapered. It will start to back off in less than 30 rounds without the tape. Originally Posted By joeIII223: Originally Posted By KalmanPhilter: I’d also recommend keeping Teflon tape away from the torque shoulder of the muzzle device. That can cock a mounting enough to get a front cap kiss / strike. Break is not tapered. It will start to back off in less than 30 rounds without the tape. What surfaces create alignment to the bore? You don’t want any materials randomly shimming those indexing surfaces. A square shoulder is a 90 degree (non) taper. Good luck. |
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Originally Posted By KalmanPhilter: What surfaces create alignment to the bore? You don’t want any materials randomly shimming those indexing surfaces. A square shoulder is a 90 degree (non) taper. Good luck. I put the teflon tape on the 16" AR to keep it from backing off. That rifle has a POI change but the groups don't change. If I am able to fix the baffle strikes in the SBR (and increase accuracy) I will Rockset it to that one and not use the tape anymore. |
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I would agree it is your can ( design ) and not your gun. I say this because I have a stainless steel F1 can I turned out on my lathe and I see no accuracy issues on my 10.3 FA 556 gun up to my semi's in to the 20 inch length. How did you make your baffles? With a press or a vise? Also I've read that freeze plug material can be all over for thickness this would also affect how they formed as far as consistancy. I had planned on using freeze plugs also but once I was told about the inconsistancies in the plugs I chose to turn out the stack on my lathe. There are ways to midigate the freeze plug problems like weighing each one and checking each for thickness. Also check each baffle hole for center and that they are all the same dia. Would also be a good idea to make sure they are all identical in the concave when forming. Good luch hope you figure it out. |
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Originally Posted By joeIII223: The gas block has clearance in the handguard, I haven't checked how much. From what I remember the can is far enough away from the handguard. I am at work and won't be able to check those until later this week. Originally Posted By joeIII223: Originally Posted By Wangstang: When mounted, how far is your gass block from contacting the handguard? How about the distance of the can to the handguard? The gas block has clearance in the handguard, I haven't checked how much. From what I remember the can is far enough away from the handguard. I am at work and won't be able to check those until later this week. Between barrel whip/harmonics and adding the extra weight on the end with the suppressor, you maybe experiencing contact with your handguard when assembled that's contributing to your problems. Take the actual hand guard tube off and leave the barrel nut, gas block and tube in place and test fire with your suppressor mounted. If things improve then you know where to start taking a closer look. If you have the old school YHM handguard I don't think it's to difficult to disassemble unless you thread locked the handguard onto the barrel nut. |
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Originally Posted By Wangstang: Between barrel whip/harmonics and adding the extra weight on the end with the suppressor, you maybe experiencing contact with your handguard when assembled that's contributing to your problems. Take the actual hand guard tube off and leave the barrel nut, gas block and tube in place and test fire with your suppressor mounted. If things improve then you know where to start taking a closer look. If you have the old school YHM handguard I don't think it's to difficult to disassemble unless you thread locked the handguard onto the barrel nut. Thanks I have a quad rail YHM on it |
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Originally Posted By OTHP: I would agree it is your can ( design ) and not your gun. I say this because I have a stainless steel F1 can I turned out on my lathe and I see no accuracy issues on my 10.3 FA 556 gun up to my semi's in to the 20 inch length. How did you make your baffles? With a press or a vise? Also I've read that freeze plug material can be all over for thickness this would also affect how they formed as far as consistancy. I had planned on using freeze plugs also but once I was told about the inconsistancies in the plugs I chose to turn out the stack on my lathe. There are ways to midigate the freeze plug problems like weighing each one and checking each for thickness. Also check each baffle hole for center and that they are all the same dia. Would also be a good idea to make sure they are all identical in the concave when forming. Good luch hope you figure it out. I drilled the holes on a Bridgeport with the supplied drill fixture and formed them with 3/8 drive Torx drivers. I was able to hold the Torx driver in the mill and form the baffles. I opened up the baffles today on the Bridgeport because of the baffle strikes, and am going to test fire tomorrow. I also designed and printed a fixture to hold the can in a Kurt vise so I could remove both ends and give it a good cleaning. I will give an AAR later. See photo of Torx drivers. Attached File |
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It appears there is enough clearance under the handguard. Nothing is crooked, my photography skills just suck. Attached File Attached File |
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After some work on my can I got to the range today I shot at 55yds prone on a bipod with Tula (I know it's not that good). I don't plan on shooting past 100yds very often. Accuracy is much improved. I will be trying it out later with some better brass cased ammo and update this thread. Thanks to everyone's advice on here. @Tejas1836 @bluedog82 @the-answer-is-42 @gtsteve03 @shooter64738 @Asylum9 @Wangstang @KalmanPhilter @OTHP ETA I put Rockset on the brake threads so the can won't back off. Attached File |
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Originally Posted By KalmanPhilter: That’s seems acceptable group size for Tula. Looks like you fixed the issue. Congrats. Thanks Your input here has helped alot! I learned alot with this can. |
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This is what @KalmanPhilter was talking about. The teflon tape is ok to have on the threads, but it should absolutely not come between the shoulders of the silencer mount and muzzle device. This can and will cause a concentricity issue (non-parallel alignment between rifle and silencer bores). I see you noted using Rocksett so I hope this part has been rectified. |
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Originally Posted By User55645: This is what @KalmanPhilter was talking about. The teflon tape is ok to have on the threads, but it should absolutely not come between the shoulders of the silencer mount and muzzle device. This can and will cause a concentricity issue (non-parallel alignment between rifle and silencer bores). https://i.imgur.com/ftu61aq.png I see you noted using Rocksett so I hope this part has been rectified. I removed the tape before Rockset. Thanks for the info. |
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Everything you need to know about the left was on display during covid . -RC03
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Wish I would of thought of this before you opened the baffles up but in the future if u have another strike, you could make a small clip in the baffles where the strike was and 180° opposite. Either way, glad you got everything worked out. |
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Originally Posted By Asylum9: Wish I would of thought of this before you opened the baffles up but in the future if u have another strike, you could make a small clip in the baffles where the strike was and 180° opposite. Either way, glad you got everything worked out. It worked out really well. I am happy with the results. I just got home from shooting at 50 yds with the can on my CMMG. AAC 55g 5.56 Looks like about a 3/4" group at 50 with an Aimpoint PRO. ETA: On the bench with a bipod, and the target photo is rotated counterclockwise 90 degrees. Attached File Attached File |
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Everything you need to know about the left was on display during covid . -RC03
Everything you need to know about the left was on display during covid . -RC03
| One of my first F1 cans was great on everything until I put it on an SBR and had the same problem. I found that while there weren't any baffle strikes, the bullets would kiss the endcap. I attributed it to greater yaw of the bullets from the shorter barrel vs longer ones. Which made the witness mark of the kissing very difficult to see. |
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Originally Posted By joeIII223: It worked out really well. I am happy with the results. I just got home from shooting at 50 yds with the can on my CMMG. AAC 55g 5.56 Looks like about a 3/4" group at 50 with an Aimpoint PRO. ETA: On the bench with a bipod, and the target photo is rotated counterclockwise 90 degrees. https://www.ar15.com/media/mediaFiles/167954/20250228_154738_jpg-3477343.JPG https://www.ar15.com/media/mediaFiles/167954/20250228_154754_jpg-3477344.JPG That's within spec for XM193. |
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Originally Posted By Wangstang: That's within spec for XM193. Thanks, good to know. Next trip I am going to put one of my scopes on it to see if some magnification will help me with accuracy, maybe a box of match ammo just to see how well the rifle will shoot. |
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Everything you need to know about the left was on display during covid . -RC03
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