Barrel harmonics and airgun accuracy

by B.B. Pelletier

Dok Watson suggested this topic. He says he had never heard of barrel harmonics til he got into airguns. Since then, he’s learned a lot. It was the same for me, Dok.

What are barrel harmonics?
A guitar string vibrates in a certain way when plucked. Those waveforms (they look like the waves in the ocean) determine the sound the guitar string makes. It turns out that many things vibrate in the same way. In a former profession, I worked with vibration dampeners to kill the vibrations made by steel beams and windows, so people could not listen in on private conversations from outside buildings!

Airgun barrels have vibration patterns, too, and they can dramatically affect the accuracy of a gun. Here’s how. When a barrel is free to vibrate any way it wants, it tends to vibrate exactly the same with every shot. As long as nothing is done to disturb the vibration patterns, such as a tuneup or using a different pellet, the barrel will try to vibrate the same every time.

The shooter has an effect!
By holding the airgun differently for every shot, you are changing the vibration patterns. It’s exactly the same as placing your finger on a guitar string at a different place. You get a different note. If you place your finger at the same place repeatedly, you will get the same note over and over, which is how guitars make music. If you hold your airgun in the same way every time, you get the same shot – meaning the pellet leaves the muzzle at the same place in the vibration pattern every time, so it tends to go to the same place downrange – every time.

But it is impossible for anyone to grip an air rifle tightly with both hands and repeat that hold shot after shot. It’s the same as trying to hold ten fingers and your shoulder and your cheek against the guitar strings in exactly the same pattern, time after time. Don’t bother trying – it’s impossible!

So, the airgunner does just the opposite – he holds the gun as loosely as he can and allows it to vibrate as much as it wants. And, if he does a good job of not influencing the airgun, his groups get better. I’m talking about all airguns – not just spring-piston guns, though those are the ones most affected.

We’re only beginning
A good hold lets the gun do its best, but that’s just where it starts. You can also tune the vibration patterns of airguns to optimize their accuracy. I have tested adjustable harmonic tuning devices on several makes of air rifles and found that they not only work – they work dramatically well! Unfortunately, there isn’t much information relating to airgun harmonic tuning, but the Browning company makes their BOSS (Ballistic Optimizing Shooting System) for firearms, and you can find lots of information about it.


The Browning BOSS is a proven way to adjust barrel harmonics.

Barrel tuning relates to length
Like guitar strings, the length of a barrel defines its vibration pattern. A tuning device like the BOSS lets the shooter make small changes in the length of the barrel, or more specifically, where the vibration nodes occur. Some airguns do this on their own through their design. A rifle with an air reservoir connected to the barrel changes vibration patterns as the reservoir pressure drops, which causes the reservoir to move. That can have a big effect on where the pellet goes, and it’s a good reason why a free-floated barrel (no contact with the gun other than at the breech) is good.

Now you understand Dok’s concern with the barrel-mounted bipod of the Crosman Nightstalker. Other barrel-mounted accessories, such as muzzlebrakes, will also change the vibration pattern. In the case of the Nightstalker, however, it seemed to make the gun MORE accurate, not less. You see, they don’t necessarily make things worse; they simply change things. The shooter has to be aware of what he’s doing to his gun when installing such accessories.

Vibration tuning is not an exact science. Even the top scientists in the free world could only guess what the effects of their work might be. We had to test each installation rigorously to determine whether we had been successful or what else had to be done. And, so it is with airguns!

29 thoughts on “Barrel harmonics and airgun accuracy

  1. OK, now this explains alot. I have only one bipod for two AF’s, A talon and a SS. Only one bipod though. I had been, till I read this, using it on both guns with no regard to where it was positioned each time. No wonder my POI varys so much by day. I need another bipod.

    You’ve also explained why some guns are just “good shooters” as you called em. Since the bore of a barrel is rarely exactly down the center each barrel is gonna be different no matter what!

    This makes so much sense out of so much Ive heard/read…great post thanx BB.



  2. turtle,

    The AirForce bipod attaches to the frame of the gun. The barrel is free-floated.

    I will be interested to hear how your dedicated bipods change things.

    B.B.


  3. I don’t know who B.B. Pelletier is, but rarely have I read so much B.S. in air gun articles as in those on that web page. I take special note that in his opening statement of the article you cite,:he promises to back up his contentions with a few facts, yet fails to actually do so.

    I decided to scan some of the other articles by this icon of air gun information and came upon his review of the notorious Gamo CFX. Mr. Pelletier informs us in his first paragraph that he is going to review this rifle, even though he has never actually SEEN, HELD OR TESTED IT ! How’s that for B.S.??? He goes on to actually describe for us how it feels, how easy it is to cock, how smooth it shoots and how accurate it is, all without ever having shot one. Amazing.

    That article pretty much puts Mr. Pelletier’s “expertise” in perspective. If you want to learn something about air guns, I suggest you avoid this :Blog” like the plague.



  4. About the CFX he never implied he himself held it or knew how it felt, he just pointed out some feature of the gun based on his own research(not experience) and the experiences reported by readers. He merely combined information gathered from several points And you have no right to rip on BB, his expertise is gathered over years and deserves respect.

    Tod


  5. Tod, Agree verbal attack was not deserved. B.B. has the courtesy and courage to post all comments, pro & con, that are within acceptable language limits, which says something positive about our moderator.The purpose of this forum is an exchange of information for all who enjoy the shooting sports. Anonymous attacks serve no purpose…………SJ


  6. Ahemmmm, OK on to airguns…

    So B.B. I had thought that the term free floating was reserved for barrels only attached at the reciever end. I had assumed the guides inside the shroud and wrapping the barrel would transfit effects of changes to the shrouds configuration as well.

    It will take several shooting sessions to try and determine the effects but we’ll see and I’ll let you know how things go with less changes.


  7. turtle,

    I’ll admit the AirForce guns are pretty strange in this respect. The bushings you refer to are, in fact, attached to the receiver, because the entire frame of all AirForce guns is considered the receiver. It’s just not attached at the barrel BREECH.

    Forward of the bushings, the barrel is supposed to be entirely free-floating, though I have seen some Talons and Condors whose muzzle caps put some pressure on the barrel. That shouldn’t matter, as long as the gun is accurate, because the barrel never heats.

    If I had a Talon or Condor with grouping problems (tightest group of JSBs larger than a dime at 30 yards) I would 1. clean the bore with JB Paste and 2. check the muzzle cap to be certain the barrel is not under pressure.

    B.B.


  8. To B.B.’attacker,If YOU are so darn smart and wish to belittle someone elses information why don’t you come on with your own blog and teach us ignoramuses what you
    know.I personaly have found B.B.’s blogs most entertaining and informative.
    Thank you B.B.
    Old shakey



  9. the world is chuck full of morons. sorry you had to bump into one more, B.B. The rest of us greatly appreciate your time, effort and experience!
    i dont have any old airguns to shoot but i did come across some old pellets covered in white oxide. B.B. will shooting these relics harm the bore of my steel barrel?


  10. cold shooter,

    I don’t think lead oxide with harm your gun, but I’m not as certain about YOU! Handling lead isn’t as dangerous as some people would have us believe, but lead oxide is already powdered and could be inhaled or injested much easier, I would think. Besides, the dimensions have changed with the oxidation.

    B.B.


  11. good point re: the shroud.

    I wouldn’t say I have grouping problems. More like a change in the groups poi…Ive heard folks who shoot competativly resight b4 a meet so It may not be so uncommon. But I’m still gonna shoot it awhile w/ no changes.


  12. Seems like everything good has some minority that has to find fault and thinks everyone should listen to him. So much in this world has been ruined by them. I see the majority here approves of what is written and discussed. So let the majority ignore the minority!!!
    This is a fine informative column and I will continue to read and use what I find to be useful and research further if need be.
    Thanks BB, Thanks for the time you put into it..


  13. I’ve purchased several airguns on BB’s advice and so far all have been exactly as described. The last one, by the way was a Crosman “NightStalker”. This gun is really fun to shoot and quite accurate. I’ve attached a red dot to it and actually increased the fun aspect. In some respects it is cheeply made but that blow back action and a puff of gas with each shot comes very close to fire arm simulation. It’s a great way to invest < $100 bucks. Keep up the good posts BB! I suspect that self appointed critic is just jealous.
    CWI



  14. bamboo007,

    We have not set up an RSS feed because of the bandwidth budget problem. I doubt we’ll do it in the future because the hits are on the increase.

    B.B.


  15. BB,

    I want you to know, and Im speaking for everyone that reads this blog,that the guy making the critics is a jealous good for nothing.I read this blog every day scince I discovered it and have learned about the sport.I think this blog is fun.BB has earned my respect.So all of us would appreciate that if you dont have something good and useful for this blog then dont participate in it.

    One question to the critic guy.If this blog is so bad, what were you doing reading it?

    BB,Keep up the great work.

    CF-X guy


  16. I have just found this blog and as far as I’m concerned it and the related web site are way ahead on common sense and clearly understood information. On the subject of the CFX ROYAL Well I also own one and I am more than pleased with it’s performance. I bought it new in Spain, it cost 86 euros in 2003.I got it home and I shot it a few times to see if I liked the feel of it, which I did .I then decided to mount an old Nikko Stirling (silver crown) 4 by 40 scope that I had on an old Barnet crossbow since 1981. To say that this scope was/is battered is an understatement. When it was on the Commando I fitted a big two cell maglite on top of the scope and a very much altered bow quiver on the side by fitting extra scope rings side ways (yep,on the scope tube) and fixing the quiver on to them. Remember, you could not buy crossbow quivers back then as I don’t think they were commercially available even in the states. So this big 175 LB Commando was looking very mean, especially when wrapped in well worn DPM strips I cut from army trousers. The .point being, this scope was dragged all over the Irish countryside in rain sleet and snow. Guess what, it works just fine on the CFX ROYAL. I rarely ever shoot past 50 meters and even a lot more below this. I zeroed it once in 03 and then I re-set it for a friend and then back again for me. My groups are never out of 25 mm and very often almost perfect.
    The article you did on HARMONICS was a great read; most of the stuff is great. I had never heard the term before but I sort of knew about it, albeit by an unknown sense. Maybe it was all that gear mounted on my crossbow that made me attend to the problems of griping weapons too tightly, it certainly works incredibly well with the GAMO CFX.
    I don’t have any lamps or lasers on the CFX, just the old scope. Someone gave it to me in the seventies .Are they still made? You never see them in magazines anymore.
    Keep up the good work B B, you’ve gained one more supporter in me.

    Good Luck, John Jones.


  17. John Jones,

    That was quite a report! You should consider a blog of your own. I know our readers love to read comments filled with so many experiences as yours is.

    Thanks,

    B.B.


  18. I have a crosman powermaster 66sb pneumatic pump rifle,they are sayin the max velocity is 690 fps but I dont believe that based on the performance,for one it will shoot straight through my fence at 8 pumps even with wad cutter pellets,somone bought it for my birth day and am new to air gunning,my question is is this common for air gun velocities to be different than advertised?I have shot 22.s a number of times so I am not new new to guns just new to airguns.



  19. Ya its just strange it seems more powerfull than advertised.Likle I said I have shot other guns so by my expierience its seems more powerfull


  20. does anyone know anything about a product to quiet a talon ss with a 24 inch barrel i read that one existed however have been unable to find one and if one does not exist then what of makeing some sort of shroud any info or sugestions would be greatly apreciated

    thanks Aaron


  21. Aaron,

    Contact D&B Sales in Topeka. 316-522-3932. They sell a bloop tube that attaches to the gun and shrouds the barrel.

    B.B.


  22. B.B. attacker; your ears “hear” harmonic vibrations. Engineers are very concerned with harmonics. Study “the Tacoma Narrows Bridge” for insight on this. You might learn something. Otherwise stay in the “bend your barrel to correct barrel droop forum”.


  23. Interesting to say the least. I'd love to know if such a contraption could be 1) Home built
    Failing which, where can I purchase?
    I own a Weihrauch 97 and group at around 8mm over 25m
    Regards
    Nick


  24. Nick,

    Because your rifle is an underlever, nobody has even built a harmonic tuner for it to my knowledge.

    The field is wide open for you to innovate.

    And 8mm at 25 M is quite a good group, don't you think?

    B.B.


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