Barrel harmonics

[Turnup]

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.

Agree with your sentiment regarding the difficulty in videoing because at relatively modest frame rates various parts of the image are captured at significantly different times. This means that a straight object which is moving relative to the camera scan pattern can appear to be bent - an effect I was startled to discover for myself when photographing aircraft with a stills camera which had a (crude) focal plane shutter. In the second linked video above the effect remains visible when filmed with different rifle orientations (wrt the scanning pattern of the camera) so I think that there is some attempt at removing that variable and I find it pretty convincing, although this does not mean that the effect is significant.

[Artfull-Bodger]

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.

It was specific to my Scorpion in regards to the Adaptor, however my HW100 groups better with the silencer fitted, so again, is that the weight of the silencer?

[RobF]

It was specific to my Scorpion in regards to the Adaptor, however my HW100 groups better with the silencer fitted, so again, is that the weight of the silencer?

Could be, but it might not be affecting harmonics, it could be just weighing the front of the rifle down. One could argue that if the end of the muzzle is moving, more mass will mean less movement for the energy imparted into it... but that isn't neccessarily the same as harmonics which is about changing a theorised vibration akin to a guitar string so that the muzzle doesn't move at the muzzle point.

Dunno, if it works go with it. But I think it's important to be mindful something else could be happening.

[Artfull-Bodger]

Could be, but it might not be affecting harmonics, it could be just weighing the front of the rifle down. One could argue that if the end of the muzzle is moving, more mass will mean less movement for the energy imparted into it... but that isn't neccessarily the same as harmonics which is about changing a theorised vibration akin to a guitar string so that the muzzle doesn't move at the muzzle point.

Dunno, if it works go with it. But I think it's important to be mindful something else could be happening.

No doubt, but what made me consider it was harmonics was the way too much or too little weight spoilt the group, that's why I went looking for info, the Scorpion barrel is floated and is 15.87mmx390mm unsupported, my Hw100 is floated and is 16mmx350mm unsupported, so the BSA has a longer unsupported length, and a slightly thinner diameter, so should exhibit less stiffness, as you say it could simply be the weight is acting as a damper, and that would be a reasonable argument, but what is it damping?

By the way the groups are shot off a gun vice that allows no movement of the stock or action.

[ballisticboy]

While the videos show the barrel/gun movement, just because the barrel/gun is moving it does not mean that the dispersion will be increased. To produce an increase in dispersion will require a change in the barrel/gun movement from shot to shot or a change in the timing of the shot exit compared to the movement otherwise you will simply get a bias not an increase in dispersion. This is where some of the barrel harmonic theories fall down as the difference in the shot exit times is insufficient to attribute the increase in dispersion to the barrel harmonic movement. This inconsistency in explaining increased dispersions is what has given rise to the barrel pressure pulse theory as the pressure pulses will move up and down the barrel at a very high rate, much quicker than the projectile. If a pressure pulse reaches the end of the barrel at the same time as the projectile then there will be an increase in yaw rate on the projectile due to a change in the projectile barrel fit at that instant. If the times are different then there will not be any increase in yaw rate and the projectile will hit in a different place on the target. Because of the high speed of the pressure pulse effects, only a very small change in projectile exit time is needed to change from the times matching to not matching. I am not entirely convinced of the pressure pulse theory for airguns as the pressures are relatively low compared to fire arms.
A movement of 2 thou in the barrel end would only give an error at 50 yards of .2 inches. A C of G offset of 4 thou in the pellet will give a large initial yaw rate and over half an inch error at the same range and so will be more critical. This is because the basic design of pellets gives a poor response to initial yaw rates when it comes to dispersions. Barrel vibrations will also give an initial yaw rate but again we have to consider variations in the yaw rates, not the yaw rate values themselves. Barrel harmonic vibrations will tend to be more consistent in their period and direction thus giving more consistent yaw rates as opposed to pellet C of G offsets which will be in random directions.
Adding moderators etc. to the muzzle end will change considerable more than just the barrel harmonics. The intermediate ballistics will be changed which may well have much more effect on dispersion than any weight or damping effect on the barrel.

[RobF]

but what is it damping?

The movement of the barrel in the firing cycle? Not like a standing wave, but the reaction to having 1000p psi injected into it? Dunno, guessing.

My walther and steyr barrels both show a POI change with just a mild 50g put on the end. One's long, 600mm the other significantly shorter. That said I'm not shooting from a vice, but it's repeatable. However, there's no horizontal change.

[transporter]

what about barrel harmonics on a springer.when the shot is taken the spring resonates cause the gun to vibrate surely this could affect the accuacy , it would be miniscule but it would still be there

[hmangphilly]

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.

it's on there to give the appearance that you know what you're doing

nobody's fooled

[bucketboy]

Until all other machanical influences have been removed (hammer Spring, hammer, valve stem, valve return spring, trigger sear, trigger spring, blah, blah, blah) surely it is not possible to determine that the vibration is due to the jet reaction and barrel harmonics?

[hareng]

Nice to see some one catching on at last.