Harmonic tuning the FX Impact - VIDEO

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Bob, I commend you for a good job on a great topic. I have followed a very similar process to get the best results achievable for a given rifle and projectile combination. I would underscore a few points and add a few more:

  1. Harmonics are far more pronounced in free floating barrels - at least in every rifle that I have had to date!
  2. 5 bar can make or break the harmonic tune - sometimes even less, I find the more power and recoil involved - the more unforgiving the harmonics will be
  3. Shoot from a stable platform - not only this, but keep the rifle's placement and orientation the same each time! I have some mods that i do to my portable shooting table, to ensure my bipod is in the same spot when I do the harmonic and velocity tune
  4. BC isn't everything - slug weight tends to me more important for long range accuracy!
  5. Shoot slower in the wind - If the wind is >7mph, the slug shooting lights out at 940 will fare better at 890-915 usually
  6. Shorter barrels will most always have less harmonic problems - these 700mm barrels can be ROUGH to tune for!
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    Dubber was also spot on when he talked about the weight of the stock affecting harmonics. Although this doesn't apply much to the Impact, he demonstrated with an AA (I think), where he showed groupings with a light synthetic stock vs a heavy wood or laminate stock; the heavier stock lessened the effects of harmonics. 

    One last thing that I would add - don't be afraid to experiment! An example of what I mean - this Crown, very pronounced harmonics at high velocities shooting slugs. I purposely tuned it so harmonics would throw off my groups, and then I put a bunch of big, beefy orings around the outside of the barrel, and guess what happened to the groups?

 
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Bob, I commend you for a good job on a great topic. I have followed a very similar process to get the best results achievable for a given rifle and projectile combination. I would underscore a few points and add a few more:

  1. Harmonics are far more pronounced in free floating barrels - at least in every rifle that I have had to date!
    [/LIST=1]
Click to expand...



  1. Interchangeable liners are not free floating. A "free floating" barrel is supported only by the receiver and doesn't make contact with anything else.

    Impact barrel liners are supported by 3 o-rings inside the barrel giving the liner 5 contact points, the barrel 2 contact points and the shroud 3 contact points. 
 
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First off thanks Bob for the video. That is why I joined AGN was for exchanging information and ideas that improve our effectiveness and enjoyment of our airguns. Next the subject of the barrel o-rings used on the barrel liner to damper harmonics. Are you shooting your rifle with them installed. It appears most are not and it seems that they are difficult to get installed uniformly spaced on the liner. Bill
 
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Yes, I'm using them. I also used them on the Crown. Just put them where you want and fix them into place so they don't move. I used two thin wraps of duct tape on the muzzle side of each oring to keep them from moving as the liner was inserted.

In this video I intentionally avoided talking about harmonics more than what was necessary, as Matt's slug video and AB101 video cover all that in great detail.

I also avoided the topics of what reg pressure, what velocity, what weight slug, what hammer spring tension, what valve setting....etc., as those answers can be found in the two videos from Matt and Ernest that I linked in the description.

Thanks for all the feedback guys.

As far as if Matt uses the valve adjuster...yes he does. This video was approved by Roelf and Matt before going public.

ADDED:

Actually I don't know for sure if Matt uses it. He mentions it in his video about the benefit of having the ability to tune by using it, but he talked about hammer spring tension more than the VA.
 
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Bob, I commend you for a good job on a great topic. I have followed a very similar process to get the best results achievable for a given rifle and projectile combination. I would underscore a few points and add a few more:

  1. Harmonics are far more pronounced in free floating barrels - at least in every rifle that I have had to date!
    [/LIST=1]
Click to expand...



  1. Interchangeable liners are not free floating. A "free floating" barrel is supported only by the receiver and doesn't make contact with anything else.

    Impact barrel liners are supported by 3 o-rings inside the barrel giving the liner 5 contact points, the barrel 2 contact points and the shroud 3 contact points. 
Click to expand...


  1. They are free-floating. The three 5.5x2mm o-rings are supposed to be there for harmonics (not support). AEAC's barrel video was also, for some time, the go-to source for STX barrel info, and I cringed a little even back then when the recommendation was essentially made to get rid of them.

    https://fxairguns.com/rifles/the-impact/

    1560716626_19207024165d06a552a12bb5.93061759_0D9DDFC9-056A-498A-90EF-05F3908A7C4D.jpeg
 
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They are free-floating. The three 5.5x2mm o-rings are supposed to be there for harmonics (not support). AEAC's barrel video was also, for some time, the go-to source for STX barrel info, and I cringed a little even back then when the recommendation was essentially made to get rid of them.
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I'm not trying to be negative here I'm just stating the fact that they are not free floating barrels by the standard definition of the term. Touching is support no matter the material. People stretch things in advertising all the time. If you remove the o-rings it's still not a free floating barrel by the standard definition because it's still supported at both ends.
 
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Bob, the only reason I asked about the valve adjustment was because in one of the videos I thought he said he just leaves it wide open. If he doesn't use it, I was wondering why. I absolutely need it to fine tune my gun but maybe he's so good at tuning that he doesn't even need it? Who knows?

Heavy... as far as the free floated barrel goes, why do you think they consider the barrel free floated even though the liner is touching the sleeve via the threaded insert at the bore as well as the 3 o rings? Do you think because although they're touching, the liner, sleeve and shroud are all acting as one free floated "unit"? 

One last question... have any of you guys done any substantial testing of the liners with and without the O-rings? I tested the gun with and without them multiple times after watching the AEAC video and didn't see any loss of or gain in accuracy at all? I'm just curious if it really makes any difference for better or worse? I'm also wondering if all of the additional contact points equals more total mass as a "unit", meaning that the liner is less affected by harmonics? If so, why not add more o rings along the length of the liner to make the harmonic tuning even easier? 

Stoti
 
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Heavy... as far as the free floated barrel goes, why do you think they consider the barrel free floated even though the liner is touching the sleeve via the threaded insert at the bore as well as the 3 o rings? Do you think because although they're touching, the liner, sleeve and shroud are all acting as one free floated "unit"? 

Stoti
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Manufacturers like to use word association to sell. It's not free floating by any stretch of the term. Even if there were no o-rings the liner and barrel are supported at both ends and the shroud is supported at 3 points. There's just no way to make that term fit. Doesn't bother me though, I love the gun and every person I've shown it to or let shoot it has loved it. It's reliable, easy to work on and capable of more accuracy than I am so what more could I ask for. I am disappointed that they confuse people with that term.
 
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Yes, I'm using them. I also used them on the Crown. Just put them where you want and fix them into place so they don't move. I used two thin wraps of duct tape on the muzzle side of each oring to keep them from moving as the liner was inserted.

In this video I intentionally avoided talking about harmonics more than what was necessary, as Matt's slug video and AB101 video cover all that in great detail.

I also avoided the topics of what reg pressure, what velocity, what weight slug, what hammer spring tension, what valve setting....etc., as those answers can be found in the two videos from Matt and Ernest that I linked in the description.

Thanks for all the feedback guys.

As far as if Matt uses the valve adjuster...yes he does. This video was approved by Roelf and Matt before going public.

ADDED:

Actually I don't know for sure if Matt uses it. He mentions it in his video about the benefit of having the ability to tune by using it, but he talked about hammer spring tension more than the VA.
Click to expand...

Bob thanks for the tip for using duct tape with the o-rings to keep them in place. Bill

PS just added the o-ring back to the barrel liner with tape to hold in place. One thing I did was to use carburetor cleaner to wipe down the exterior of the liner and install the o-ring without lube. That made them really grip the liner very well, then lube the outside with some silicone to ease them back into the barrel.
 
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Okay so I tried out Bobs method, not that my gun wasn't good with the 25g Monsters in the first place, I just wanted to see if it would be better.

So I set out at 25 yards as advised, 25g Monster & 34g Beast (2 different batches of each just for good measure) and my big regulator direct from the 12L carbon bottle to avoid constant refilling.

First I tried the 600mm B pellet Liner, averaging 966FPS, shot all variations. Then I left the settings and tried the 700mm barrel the following things were obvious;

1) The groups tightened up with both pellet types.

2) The setting still improved the groups even after I changed barrel.

AND then I decided to try the 26g VK slugs just for fun even though I was using a 700mm B liner,

1) 5 shot GROUPS WITH THE 600mm SLUG LINER PREVIOUSLY SHOT 25 YARDS (NO HARMONIC TUNING)

1560792793_11421695265d07ced9b72587.40799257_IMG_1089.jpg




2) 5 shot Groups with the 700mm B PELLET LINER and 26g VK SLUGS (AFTER HARMONIC TUNING WITH THE 25G MONSTER PELLETS-ALL SETTINGS THE SAME)

1560792921_1908811645d07cf591c5ac1.89851225_IMG_1298.jpg


1560793009_4043005885d07cfb1b36642.62665426_IMG_1297.jpg


986 FPS

To say I was surprised with the slug performance is an understatement, off to shoot 100 yards with Laity tomorrow, fingers crossed this pans out at longer range, I shot a couple more groups at 25 just to prove it wasn't a fluke, same result.

Tethering at 180 bar.

1560793261_4846729415d07d0ad246925.69302232_IMG_1294.jpg


1560793284_18761607005d07d0c45d9be9.28663781_IMG_1296.jpg



 
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That's impressive Mark! 

Here's another tidbit....the accuracy nodes can generally be found 20fps apart with 22 caliber. A good tune on one weight can often be good with a different weight as has been my experience. 

So it seems if I'm reading your results correctly, you got these results at 966 and 986fps? I'm not surprised being they are 20fps apart.

I hope this gives you tighter groups down range. Let us know please. 

🙂
 
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If you have a crown (that doesn’t include the valve limit adjustment) something else you can try that can effect vibration/harmonics node is the tightening or loosening the threaded tensioning screw for the barrel liner! I did this I my crown, I found that it shot the 15.9 jsb’s much better than the 18.1’s with the standard tune from factory but I wanted to push the heavier pellets @ the same speed so I played with the hammer adjustment and Reg psi. etc. was ok but still not the accuracy I wanted so started playing with shroud location, o-rings on/off etc. then went to indexing the barrel when I noticed that the barrel tension Had an effect on accuracy! Also I felt it better to leave o-rings in place and shroud fully retracted with an o-ring between shroud & action! Sorry for being long winded, but something to try!
 
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Well done bob:)

I like you mention the difference on speed/power tuning, and harmonic tuning. Guess many mix thouse 2 terms. Some adjust for low extreme spread close to the desired speed, and leave it there. That is not harmonic tuning at all, it is just numbers on a chrony. Ernest actually mention on his video, when he lowers the speed on the last step, that we should be shooting on target. So if some doeas not take notice, it can be easy to forget. I am not an expert, but since I mostly adjust my guns shooting on my 25m backyard range, shooting pellets, I have also noticed the velocity often have to be dropped lower than intended, from the true max, to get better accuracy.

When I first started out adjusting my guns, I first shot indoors offhand true a chrony, until the numbers looked good. And then when I shot on range outside without chrony, and the result was not good enough, I simply believed I was shooting with to high or to low velocity. I have then learned to shoot over the chrony, and at the target at the same time:) 

 
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