Barrel harmonics

[Artfull-Bodger]

The video here is a bit of an eye opener as to the barrel harmonics of an airgun. https://www.youtube.com/watch?v=RftoBqi_y-M&t=169s

What the guy has done is attach a laser to the end of his barrel and on firing filmed the laser spot on the target with surprising results, now bear in mind this is FAC rated so will be more pronounced but it gives a clear idea of how much movement and therefore the poi there is with an air rifle, also how useful it could be to experiment with muzzle weights to tune the barrel.

[krisko]

i think it is the whole gun moving, everybody knows the hw100 is rubbish at fac, because of the barrel and the small pre chamber.

people try to find and explanation for poor grouping, i am not conviced that you can bend the 15-16mm barrel by air pressure. high power does recoil yes but other guns can still group decently.

[blooregard]

people try to find and explanation for poor grouping, i am not conviced that you can bend the 15-16mm barrel by air pressure. high power does recoil yes but other guns can still group decently.

Newton and Pythagorus would probably disagree.

[Artfull-Bodger]

i think it is the whole gun moving, everybody knows the hw100 is rubbish at fac, because of the barrel and the small pre chamber.

people try to find and explanation for poor grouping, i am not conviced that you can bend the 15-16mm barrel by air pressure. high power does recoil yes but other guns can still group decently.

watch the multiple target shot at the end, the rifle is benched , they all exhibit the same movement, take a look at this if you think barrels cant move - https://www.youtube.com/watch?v=NR6AW3rQrTY, https://www.youtube.com/watch?v=FaW_Hs0B79c

what you have to remember is that target is at 30m so the tiny amount of movement at the barrel is amplified by the range.

[lensman57]

watch the multiple target shot at the end, the rifle is benched , they all exhibit the same movement, take a look at this if you think barrels cant move - https://www.youtube.com/watch?v=NR6AW3rQrTY, https://www.youtube.com/watch?v=FaW_Hs0B79c

what you have to remember is that target is at 30m so the tiny amount of movement at the barrel is amplified by the range.

I am not quite sure if the problem with some HW FACs is not related to the very long 24" barrel. Has anyone tried the gun with the shorter 16" barrel? It may not make 48J of ME but it could help its consistency.

A.G

[Matt]

I didn't believe in it until Jon Harris modded my Anschutz 9003 with a harmonic tuner, made a big difference turned average groups into great groups overall more consistent groupings.

Still can't get my head round it but am convinced it works.


Matt

[ballisticboy]

Videos which purport to show barrel harmonics are in the main very unconvincing. There are always important details of the experimental techniques missing many of which could be vital to a properly controlled experiment. They also miss the main point of any barrel movement and its effect on the pellet flight. Just because a barrel is vibrating it does not mean this will lead to an increase in dispersion, that will require a variability in the vibration which the videos do not show. Much of the barrel vibration shown will produce a bias in the mean point of impact not an increase in dispersion. The barrel harmonics will not have gross changes from shot to shot so should not produce large dispersion patterns. The difference in timing of pellet barrel exit is also too small to explain any large increase in dispersion due to barrel harmonics. There are other effects of the air pressure and pellet movement on barrels which can give rise to very high frequency barrel changes which affect pellet barrel fit and could lead to increases in dispersion but they are nothing to do with barrel harmonics.
I have said it before but really YouTube is not a good place to try to obtain accurate information on the science of shooting.

[Geezer]

Videos which purport to show barrel harmonics are in the main very unconvincing. There are always important details of the experimental techniques missing many of which could be vital to a properly controlled experiment. They also miss the main point of any barrel movement and its effect on the pellet flight. Just because a barrel is vibrating it does not mean this will lead to an increase in dispersion, that will require a variability in the vibration which the videos do not show. Much of the barrel vibration shown will produce a bias in the mean point of impact not an increase in dispersion. The barrel harmonics will not have gross changes from shot to shot so should not produce large dispersion patterns. The difference in timing of pellet barrel exit is also too small to explain any large increase in dispersion due to barrel harmonics. There are other effects of the air pressure and pellet movement on barrels which can give rise to very high frequency barrel changes which affect pellet barrel fit and could lead to increases in dispersion but they are nothing to do with barrel harmonics.
I have said it before but really YouTube is not a good place to try to obtain accurate information on the science of shooting.

I don't disagree.

My own view is that barrel harmonics are really important for powerful firearms.

They are less important for low-powered airguns.

But they are not irrelevant.

Views?

[blooregard]

I think that barrel harmonics are pretty crucial, more so in lower powered guns where the projectile spends more time in the barrel. It only needs a couple of thou of movement at the muzzle to prevent a single hole group at 30 yards.

The trick is to get the same amount of movement in everyshot, hence why (I think) shooters tend report that tuning an air stripper results in an increase in accuracy.

[lensman57]

I am sure that a few judiciously placed bands of Sorbothane on the barrel will kill off most of the vibrations and turn them into heat. I used to do this on expensive tone arms to kill off the residual colouring of the sound due to secondary sound waves travelling down the arm. It can't be that different..

A.G

[rogb]

My barrel is permanently bonded inside a CF tube (from the factory). It has a "plug in" stripper/end plug fixed securely at the muzzle end of the tube, which overhangs the barrel by a couple of inches, stiffening up and damping the open tube end.
It is also fixed very firmly at the breech end. I have twatted it against many trees and not lost zero.

I don't think there is too much barrel vibration noticeable due to the damping/stiffening effect of the CF/bonding agent. The barrel is also quite short too.

It's a very accurate gun so I tend to think that barrel harmonics (vibration) may not affect grouping that much.

What say you, Ballisticboy?

[Artfull-Bodger]

Videos which purport to show barrel harmonics are in the main very unconvincing. There are always important details of the experimental techniques missing many of which could be vital to a properly controlled experiment. They also miss the main point of any barrel movement and its effect on the pellet flight. Just because a barrel is vibrating it does not mean this will lead to an increase in dispersion, that will require a variability in the vibration which the videos do not show. Much of the barrel vibration shown will produce a bias in the mean point of impact not an increase in dispersion. The barrel harmonics will not have gross changes from shot to shot so should not produce large dispersion patterns. The difference in timing of pellet barrel exit is also too small to explain any large increase in dispersion due to barrel harmonics. There are other effects of the air pressure and pellet movement on barrels which can give rise to very high frequency barrel changes which affect pellet barrel fit and could lead to increases in dispersion but they are nothing to do with barrel harmonics.
I have said it before but really YouTube is not a good place to try to obtain accurate information on the science of shooting.

What the video does is give a visual example of the way a barrel can move on firing rather than a scientific measurement that is applied to all rifles, it's a visualisation of a principle which helps people understand, I think your trying to be too specific here, barrel vibration/harmonics is an issue on some rifles the fact 10m guys use barrel tuners is evidence of that, but to the layman a simple demonstration of the principle is worth a thousand words of technobabble.

[RobF]

the fact 10m guys use barrel tuners is evidence of that

They don't. What you perhaps see are barrel weights to balance the rifle. Even the top guys have just only got into batch testing. 10m for an air rifle is not much test of it's mechanical ability and much more about the shooter. The bull is effectively 5mm wide. If you're having trouble hitting that then it's not going to be an unproven theory that's going to help you out.

It's more prevailent in other longer range disciplines, but as BB has said, there's really not a good scientific approach to the testing that apparently shows it.

I've got a weight at a point on my comp rig barrel. I'm not wholly convinced about it's effect, and despite trouble shooting reg's, pellets, brakes, valves, springs etc, it has never moved even though i've changed a lot of other items. The reason for that is that when everything is as it should be, it's not making any difference. The groups are as good as I can get them. It's there still because I have to remove a brake or barrel to get it off.

[Artfull-Bodger]

They don't. What you perhaps see are barrel weights to balance the rifle. Even the top guys have just only got into batch testing. 10m for an air rifle is not much test of it's mechanical ability and much more about the shooter. The bull is effectively 5mm wide. If you're having trouble hitting that then it's not going to be an unproven theory that's going to help you out.

It's more prevailent in other longer range disciplines, but as BB has said, there's really not a good scientific approach to the testing that apparently shows it.

I've got a weight at a point on my comp rig barrel. I'm not wholly convinced about it's effect, and despite trouble shooting reg's, pellets, brakes, valves, springs etc, it has never moved even though i've changed a lot of other items. The reason for that is that when everything is as it should be, it's not making any difference. The groups are as good as I can get them. It's there still because I have to remove a brake or barrel to get it off.

I think your right, it seems the tuners I was looking at were for rimfire.

One experiment I did was fitting an air stripper to my BSA Scorpion, which was not grouping well, but the groups got worse, no matter what I did to the cone, so I removed the cone and the groups improved, initially I thought this was the cone clipping, but on examination I could see no possible way it could clip, so I made an alloy cone of the same dimensions instead of a brass one, then tried again and this time there was little change in the group, by this time I was beginning to suspect the weight was the issue so I made an adaptor for the end of the barrel with a reduced spigot like a back to front top hat which allowed me to fit 1/2" washers on the adaptor held on by a nut.

End result of this was off a rest at 50yds I was able to open and close the group dependant on how many washers were on the adaptor, as I added washers the groups initially got worse then improved as more were added, up to a point when it started to open up, so I fiddled about until I got a consistent group with a particular number of washers, I then weighed the adaptor and made a stainless steel muzzle weight to that weight, end result is I now get far better groups with my Scorpion.

Encouraged by this I tried the adaptor on my HW100, and guess what, it didn't work, the HW100 shot it's best groups with the silencer fitter.

You live and learn

[RobF]

I've never seen groups improve with something added to the barrel, not when the shooter is removed from the equation, but i've seen bad groups occur with no visible signs of clipping, and we take great pains to ensure that brakes are central when we fit them. Not sure what it is. What I do know is that tiny almost invisible bits of junk on the bore of something on the muzzle can have a considerable effect.

Yep i've seen the barrel tuners. It's in my airgun voodoo box marked investigate later. But to date, my big improvements in groups have been batch testing, and getting the gun consistent.