Suppressor and accuracy?

[BenY 2013]

So I've done some research and I'm not coming up with much. What makes a suppressor accurate? Obviously concentric building over the entire thing, but what else? Can anything else be done to help with accuracy? Put my Form 1 on my AR and shot a group over 1moa. I haven't shot the AR enough to know the exact accuracy of it. But the 1st group I shot unsuppressed was around 1/2moa. Is there anything I can do to fix this? The baffles are clipped cones with a flatter blast baffle.

One thing I worry about is someone helped me thread the main tube and it may not have been set up totally concentric. I was excited and in a hurry and forgot to throw an indicator on the collet and check it. Obviously I should have checked that more.. We were using a precision collet to hold the tube on the CNC lathe. Do you guys normally do it on a 4 jaw chuck so you can dial in the bore?

One more thing I noticed when I shot was that I got hit with a lot of gas through the ejection port. Not sure if that would have anything to do with accuracy or not.

Ben

[Capt. Link.]

Make sure the suppressor is tight against the barrels torque shoulder.
1)Look down the barrel from chamber end every thing should "look" centered.
2)A laser bore site tool should be a perfect dot on the wall.
3)A range rod placed in bore should be centered in muzzle cap of can.
4)Do a run out test using a threaded stub barrel that runs true on lathe and mount suppressor.Rotate the chuck with a indicator touching the muzzle caps bore.If this test dose not reveal excessive run out then the problem is the barrel threading or torque shoulder of rifle.
If your reading is not .000 then use trig to calculate if your baffle clearance is enough for the length of the suppressor.
Rarely will the harmonic change cause accuracy problems due to suppressor mass.Most time the accuracy will be better with suppressor installed.

[a_canadian]

You might want to check out this guy's adventure in precision suppression:
viewtopic.php?f=10&t=131173
Sounds like he's still working on it, making yet another can, but his triple-clipped cones seem to have done the job (so long as his can stayed on tight) of reducing group size through symmetrical clipping, while suppressing well.

[CMV]

First off, at what range & with what ammo?

If it's 50 yds go longer - 50 is too close to call anything on an AR. I see that all the time on the 300 BLK forum - guys raving about their 50 yd accuracy.

Also what is the ammo? I'll draw fire for this I'm sure, but FMJBT factory loads will not shoot MOA from an AR - or at least very few ARs will do it. I can shoot groups well under 2" @ 300 yds with my handloads but won't do the same with ball ammo. Interwebs full of guys claiming MOA with various bulk ammo and either they are [grossly] exaggerating or don't understand what MOA means.

3, 5, or 7 shot groups? 3-shot groups aren't outstanding data points.

Hanging weight off the end of a barrel can have an effect on accuracy. My 16" Stag upper actually groups a little tighter with the suppressor attached. But a change in barrel harmonics can easily effect accuracy.

More ejection port debris is typical. My 300 BLK AR is so bad with suppressed subs I was unable to run a 45° micro red dot because it just throws way too much crap in my face. My .223 isn't nearly as bad, but there will be more crud in the upper receiver & coming thru the ejection port suppressed. If you run an adj gas block you can tune that for some improvement.

[BenY 2013]

I'll do some of these tests to see how concentric my bore is to the tube. I have looked down the barrel with the suppressor attached and it all looked straight. But I'll do more conclusive tests!

I am using Fiocchi 50gr Vmax same I shot the sub MOA group with. And yes all this testing is being done at 100yds, 50yds is for rimfire. I'm shooting from the prone with a rear bag. I appreciate all the help, hope I can get this worked out!

Ben

[a_canadian]

Try using a black Sharpie on the bore of every baffle before testing. Relatively easy to detect scraping on that.

[sub-sonic]

what barrel profile do you have
what handguards do you have

[CMV]

I would say it's something as simple as your barrel harmonics w/o the extra weight at the end are better suited the 50 gr VMAX than with the extra weight. Try some 40 or 55 gr. Or if you can find something loaded with the 53 gr VMAX bullet try it since it has a very different profile than the 50 or 55 gr VMAX.

If you're only supporting with a rear bag I'd suggest that you now have a longer and differently balanced end floating around and that alone can easily account for groups opening up. I mostly shoot off one bag as well, but I use a front bag for the rest. It's much easier to get more of your body in contact with the rear of the rifle.

Do you have one of the .223 cartridge type boresighters?


If so, CPT Link gave me a great idea of how to check mine with that. Chamber that & then put a piece of paper over the muzzle. It will show precisely where the laser dot is in relation to the exit hole.

[Capt. Link.]

Now I remember what those rolling papers were for!

[BenY 2013]

My barrel is a medium contour and hand guard is an Odin Works Kmod free float. I'm gonna try some of the suggestions mentioned tomorrow. Sadly I don't have a laser bore sight. I like that idea!

Ben

[L1A1Rocker]

You might want to check out this guy's adventure in precision suppression:
viewtopic.php?f=10&t=131173
Sounds like he's still working on it, making yet another can, but his triple-clipped cones seem to have done the job (so long as his can stayed on tight) of reducing group size through symmetrical clipping, while suppressing well.

I'm really liking the "triple-clip" design. I think I'll go with that in my upcoming builds.

[gunny50]

You might want to check out this guy's adventure in precision suppression:
viewtopic.php?f=10&t=131173
Sounds like he's still working on it, making yet another can, but his triple-clipped cones seem to have done the job (so long as his can stayed on tight) of reducing group size through symmetrical clipping, while suppressing well.

I'm really liking the "triple-clip" design. I think I'll go with that in my upcoming builds.

[BenY 2013]

So I finally got around to testing it today. I had a barrel setup in the lathe that had just been threaded. I screwed my can onto the muzzle and checked it with an indicator. It is about .015" out. So I figure that is my problem... Anything I can do, besides re-make the tube?

Ben

[Capt. Link.]

So I finally got around to testing it today. I had a barrel setup in the lathe that had just been threaded. I screwed my can onto the muzzle and checked it with an indicator. It is about .015" out. So I figure that is my problem... Anything I can do, besides re-make the tube?

Ben

Re-machine the end cap.

[CMV]

You sure the barrel was true in the lathe? If you put a long pin gauge in the bore & then run the carriage back an inch or two is still at the same runout?

I can't explain why this happens, but whenever I indicate a barrel in a 4-jaw I can get it dead nuts right at the muzzle, but then when I run the carriage back a couple inches, I'm showing runout. It takes me a considerable amount of tinkering adjusting not only at the chuck but also at the spider to get it true. Not something I do every day, not something I'm well practiced at doing, and I probably don't know the most efficient way to go about doing it, but it takes me a good half hour (if not longer) to get indicated in on a rifle bore. One of the most time-consuming setups I've done.

Anyway, I wouldn't be surprised if that's where your runout is coming from depending on how you setup & indicated the barrel in the first place. Get one of those cartridge type laser boresighters. You'll use for other uses eventually or else trade it away on armslist when you're done with it. That's got to be the simplest way to check it.

Kind of a PIA holding this & the camera & fighting with it to focus, but you get the idea. Laser boresight, tissue paper over exit hole. Will show you how well you're aligned to the rifle's bore.

[gixxerpilot750]

I'm not a gunsmith and have not threaded any barrels myself, but I've been fortunate enough to watch over the shoulder of some really good benchrest shooters as they chambered barrels. Reading the previous post, it sounds like you're already measuring the bore at multiple points along a range rod from the muzzle end. As far as I understand this, a laser bore sighter will not 100% accurately indicate concentricity....it will get you in the ball park, but isn't perfect.

Many barrels aren't straight. By this I mean that immediately after the moment of ignition, the bullet doesn't travel in a straight line out the barrel. If you were to set up a barrel between two centers and spin it, the outside profile of the barrel might show no runout, but the bore might look like a jump rope going round and round. So if the barrel that we're imagining has a bore that looks like a jump rope, and we stop it at the top of its rotation (12 o'clock), it looks like a rainbow or arch. Laser bore sighters only point "straight" from the chamber or the left end (at least in my imagination) of the barrel. So if we put one in the barrel we are imagining, it's going to indicate that the bore is "straight" relative to the chamber, not showing us the hump in the middle. A bullet fired through our imagination barrel is going to be traveling downward (6 o'clock) as it leaves the muzzle when the laser says it should still be pointed towards 12 oclock.

[Kuraki]

I just posted this in my build thread but it may apply here. This is a 15 shot group, 5 suppressed, then 5 unsuppressed, then 5 more suppressed out of my 6.5x55 at 100 yards. Prior to building the can, I shot 5, 5 shot groups with the rifle that averaged .6 MOA. This 15 shot group is about 1.5" extreme spread. The group on the bottom right was a new load I was testing using the bar code as POA.

[T-Rex]

My only gripe with this method is the laser needs to calibrated to the absolute center-line of the bore, prior to this test. Not unobtainable, but maybe missed by some.

I do a similar method, but instead of a laser, I use a bore-light adapter for my little Pelican 1900 light.
Just looking down the muzzle towards the light will give you your answer. Move the light, ever so slightly, and anything nonuniform will be very evident.

[Capt. Link.]

gixxerpilot750 First welcome.
I'm am a gunsmith and you are correct that many barrels are not straight.The one point you are not thinking about is the last few inches of the barrel this determines the actual path.CMV is using a long gauge pin so he is doing it the right way with precise results.A non straight bore normally will "walk" as it warms up but this will not affect alinement.
The collimation of the any laser is necessary like any tool.The test will determine how accurate the threading is and how straight the suppressor is in relationship to the chamber.While not a laboratory test the results will quickly reveal a poor job.Keep in mind the length and aperture of the suppressor will determine if any inaccuracy in machining will cause problems.The use of Pythagorean theory is a valuable tool for this.
Kuraki
The addition of or the removal of weight can affect harmonics of a barrel you need to determine which.If your gun was .6 and now 1.5 did any other work in between happen like threading the barrel.When you remove material from the muzzle the bore will flare affecting accuracy.If it was threaded between centers and not properly re-crowned that can do it as well.My own experience is that its not harmonics unless the barrel is light compared to the suppressors weight.
Happy holidays CL

[Kuraki]

snip
Kuraki
The addition of or the removal of weight can affect harmonics of a barrel you need to determine which.If your gun was .6 and now 1.5 did any other work in between happen like threading the barrel.When you remove material from the muzzle the bore will flare affecting accuracy.If it was threaded between centers and not properly re-crowned that can do it as well.My own experience is that its not harmonics unless the barrel is light compared to the suppressors weight.
Happy holidays CL

I should have posted the 5, 5 shot groups I did that average .6. One of them exceeds 1 MOA.

I believe if I would have shot the 3, 5 shot groups (suppressed and unsuppressed) into separate groupings each, they would have been much closer to .6 MOA average.

In the group of 15, the left most 10 shots were suppressed, and the right most unsuppressed, and the aggregate grouping of all 15 rounds is including POI shift. I didn't intend to measure the average accuracy of the rifle, more the consistency between removing and reinstalling the can. Perhaps that was a poor test.

Nothing on the barrel changed. It was crowned and threaded when I built it.

I will do another test, and simply mirror the original accuracy test of five, five shot groups. With the addition of removing, and replacing the suppressor between each grouping. I believe this will show that the POI may drift around somewhat, but that it's still a .6 MOA average rifle.