Harmonic Barrel Tuners - Any Experience?

[rsterne]

I am diving into the deep end of barrel tuners, designed to alter the harmonics of a barrel to tune it to the pellet and velocity, not unlike what rimfire shooters are doing.... Centerfire reloaders have the opposite approach of tuning the velocity to the barrel harmonics, which can also be done with airguns, of course.... but I'm greedy on velocity and want to try the tuner approach.... Most of these consist of a movable weight, threaded onto a carrier that in turn is threaded onto the barrel (or sometimes clamped).... The threads between the weight and the carrier are usually quite fine, 32 TPI or more, so that the weight can be moved as little as 0.0005" repeatably, using a Vernier scale engraved on the carrier and weight....

My questions, for those that have tried these devices, are:

1. How well do they work (group size reduction)?
2. What does the moveable weight weigh?
3. How fine an adjustment do you find that makes a difference?
4. Do you find any difference between tuners that are behind the muzzle, compared to extended past the muzzle?....

For those using a weight that slides along mid-barrel, (like a Limbsaver) the first three questions still apply?.... Thanks for any help you can give....

Bob

[MichaelM]

Wow Bob... your really getting into the wizardry side of things on this can of worms your opening.... lol

And this is one area where I can actually claim bit of expertise as harmonics are harmonics and what works for powder burners will work for airguns as well....

here is the quick answer for those that dont want to read everything I type....

THEY ALL WORK WELL!!!!

now we got that out of the way lets cover the basics..... i would probably classify all the different methods into 4 major categories.. Freefloat, Pressure/tension, weights, Absorbing materials...

Freefloating we are all familiar with and use it a lot of ways(artillery hold is actually just another take on the entire thing as well) generally it will work well across a larger range of loads and is the least finicky..  but it generally wont give the BEST results with a given load...


Pressure bedding/tension setups tend to be very popular with the small bore crowd and would also be a good option for airgun with the thinner barrels..... they are pretty finicky though and require a good torque driver of some kind to get repeatable results... change of just a couple ounces of torque can make it go from horrible to unbelievable back to horrible again....  great option for someone not wanting a big weight hanging off the barrel OR if they would rather have a shroud or stripper of some kind and most of those could be incorporated into a tension setup... pressure bedded usually has a free floated barrel EXCEPT for a small bump at the end of the stock.... the action is torqued down and the bump puts pressure on the barrel changing its harmonics.... have also see amazing results but its just as finicky or maybe more so then a true tension setup.... on wood stocks changes in weather can drastically change the torque effecting things...  if a tensioned setup is released for some reason... it WILL have to be retuned... just setting it back to xx amount of torque probably wont be exactly where it was last time even if you use a good lubricant to cut down on the "sticksion" of the threads...

Weighted setups... as finicky as tensioned  setups but MAYBE (with really REALLY precise threads and no runout)  its much easier to repeat settings across loadings without a lot of tools and and such... after the sweet spot is found the turns out and what part of the turn can be recorded and set back to what each load likes... they are probably the easier to make repeatable and chang between loadss.... if you dont mind a big weight off the end of the barrel.... lighter the weight the more "resolution" you should have.....

dampening materials.... I honestly dont have a lot of experiance with these as I never really liked the aesthetics of them... But they would be similiar to freefloating....with a little adjustablility ... about the same results as frree floating giving you a wider range of GOOD results but maybe not the BEST results....



so freefloating/dampening  materials are the simplest... generally giving good results over a larger spectrum... While tensioned and weighted setups will give you the BEST results for a given loading


personally... for a target rifle I think a weighted setup would be king... would even allow you to make small adjustments between different lots of pellets verty easily with a few tweaks.....

hunting rifles where noise may be a factor tensioned setups are awesome because they can be incorporated into shrouded setups very easily..... (though... you COULD make a weighted "ldc" with a scaled threading system that would work pretty sweet too but I would think over time the dust collecting in it would probably change things.....) shrug dunno never tried anything like that...

[MichaelM]

gosh... really even everything I typed doesnt really scratch it.... its all both so simple yet so much variation.... best advise is pick the one you want to use and then just go with it till you get the results you wants.... they all work ... some are just better or worse depending on the situation they are being used in.... 

[rsterne]

Thanks for all of that, Michael, much appreciated.... I have a tensioning setup on several of my guns now, and need more time to play with them.... In order to widen out the sweet spot, I am using Belleville washers at the muzzle, which are compressed by the tensioning nut.... in the hopes that temperature change won't have as much effect.... It also should allow setting to a given tension rather easily and repeatably.... We are not allowed LDCs or shrouds that reduce the report in Canada, so that is not an issue here.... The other style I would like to play with is a moveable muzzle weight.... I have many guns which have a Hatsan Air Stripper on them, and they are 24mm OD, which I can thread to 15/16"- 28 and I can get a tap and die of that size without spending a fortune.... I am contemplating making a threaded brass weight, split, with a SHCS to lock it in place (like a threaded shaft collar), that will thread on the Hatsan Stripper and can be adjusted fore-and-aft.... What do you think of that idea?.... How much weight do you think would be needed to cover the range required with, say, 1/4" (7 turns) total movement?....

EDIT: I already ordered the tap and die.... too late now!.... 10 deg. is 0.001".... 

Bob

[MichaelM]

Dang it...  I typed out a reply and before I could hit post my computer decided it was time to update windows.....  Ugh windows 10 is getting on my nerves......


ANYWAYS...  Look up the B.O.S.S system by Browning ....  Also a few others like supertuner....  Google adjustable muzzle weight or something...  Lots of different results....

I would think maybe 2-4 oz with half inch to an inch of total travel??? 



I am guessing on the total weight as I have no idea but most seem to have a half inch of travel or so...

As handy as you are and with your skills you would probably be better off making something from scratch.... 

My biggest concerns would be thread accuracy.....  Dunno if a standard threading would be close enough tolerance to be as accurate as you want.....  Unless your not worried about strict repeatability then anything would work....

[rsterne]

Repeatability isn't too important, and I realize that needs near-perfect threads.... Anyway, once I have the tap and die I can make any attachment at any length, if the Hatsan Stripper idea won't work.... Having the split weight and locking screw makes the threads basically tight anyway.... I got a tap and die, shipped, for $64 CDN, pretty decent deal, IMO.... Now I just need some 1.5" brass rod for the weight.... Brass weighs 4.96 oz. per cu.in... so with a 1.5" OD and a 15/16" ID (1.08 sq.in.) that works out to about 3/4" long for 4 oz.... seems workable.... 

Bob

[MichaelM]

Bob if it's a split die...  You can always tap your material then open die up as far is it will go to make it cut slightly oversize.....  Might help with the backlash a bit in the threads...  There are so many ways to approach the weight....  And they all work lol....  Go with what you see in your head and it should work!

[Motorhead]

Also research the Wiscombe H.O.T.S system that was very successful.

[rsterne]

Fixed die, but the nut (collar weight) will be split with a lock bolt....

Bob

[Gerard]

My only experiment with a barrel weight so far was on a little IZH MP-61 for my son, which was kind of giving shotgun patterns at 10 metres. Groups were about 1" diameter from a light rest on a sand bag. Since that rifle has a reputation for surprising accuracy considering how cheap it is I figured it was weird barrel harmonics I introduced by first chopping a bit off the barrel length (trying to lighten and shorten it for the little guy) then using epoxy to glue a CF tube over it in hope of stiffening. It's stiff, but must just jump around enough to spray pellets too widely in every direction. Hits on the 10 were rare.

So I added a bronze ring with set screw and shot lots of groups at 10 metres with the thing set at various increments back from the muzzle. Finally settled on about 22mm back from the crown as this shrank the groups by about 40%, about as good as seems possible from this rather unruly springer. The bronze weight weighs 40 grams including set screw. Further forward opened up the groups a little. Further back opened them up a lot. Placement at or near the middle of the barrel made little difference in group sizes.



While I haven't tried with anything more powerful, my guess would be that the considerable disruption of stability of the barrel coming from the rough spring-piston action cause proportionally more barrel whip than with most any PCP. So more weight may be necessary, but I'd probably start at a similar weight on a PCP then go bigger if it proved inadequate. Tuning vibrating metal things is an interesting pursuit, something which will no doubt benefit from your patient analytical approach to such things and facility with numbers. But generally speaking, this barrel tuning thing is like making a tuning fork stop ringing by adding a weight. As such, my suggestion would be that if your barrel isn't locked into the rifle, try first clamping it into a vise with support similar to what the upper will give it, and ring it. Strike it at various points, not just the muzzle end. Listen to the vibration, both loudness and duration. Then clamp something to it, a small metal clamp perhaps. Move that clamp around and keep ringing the barrel, striking it at the place which gave the loudest ring. Listen for changes. When you find a place where the clamped weight almost entirely damps the ringing of the barrel, you may have found a good place for a barrel weight. And of course if you're doing such experiments, testing with a secondary weight near the middle of the barrel might be merited, as that's something some benchrest guys are using. Striking the barrel with a wooden mallet or similar won't be definitive, but it should give you a very good idea just how this piece of steel likes to move and how to stop it.

[rsterne]

Here is what I have decided to try....



The blue is a threaded brass collar, split and locked by a 6-32 SHCS, and will weigh about 4 oz.... The thread size is chosen so that I can thread the outside of a Hatsan Air Stripper, or make a muzzle attachment as shown in the drawing above.... Each 10 deg. increment will move the weight 0.001".... Here is a Hatsan stripper, the forward part is 24mm, which I can thread 15/16"-28....



The one in that photo above is on my Hayabusa 7mm, and is being used as the nut to compress the Belleville Washers to tension the barrel.... I can also replace the air stripper with a simple mount as drawn above to tension the Bellevilles.... If it turns out that I can't shrink the groups enough just with tension, then the weight will allow me to fine tune the harmonics.... at least that's the theory....

Bob

[SpiralGroove]

Thanks Bob/Guys,
I may experiment with a brass ring/set-screw approach to see what improvements can be seen at 13 yards
Kirk

[moorepower]

You can always make one like the Harrels tuner which allows you to use different weight collars on it. Tuners work best tuned to a specific velocity once set, to counter harmonics at that velocity. Using an inner threaded collar will work alot better as it will allow you to use a more repeatable finer adjustment. In my opinion adjusting velocity of a pellet within a pellets operating range has more to do with harmonics than it does to anything else. The longer the dwell and the heavier the pellet the better a tuner will work. The big question is will it be worth the effort, but I think you are more interested in knowing if it works than how well it works. The journey is more interesting than the final destination to the inquisitive soul. As far as weight, compared to rimfire, I have no idea, but I am guessing 4-6oz. For the adjustable outside collar would be a good place to start. On a tuned .22lr bench gun the average shooter might not see an improvement untill you start measuring the target.

[Slavia]

The front sight on my Slavia 631 sits in a long dovetail at the muzzle.  One day I removed it, and when I put it back the accuracy went all to heck.  Just the front sight position made a difference.  That gun now has a brake made from 5" of aluminum paintball barrel, and position makes a difference.  I shot groups, changing the position by 0.015" each time.  I then plotted the data points in MS Excel and used the "best fit" function to generate a curve that represented group diameter as a function of brake position.  In looking at one "cycle," (bad to good to bad again) the curve was roughly sinusoidal, with a "wavelength" of positions spanning about 1/4".  I used the curve to interpolate the final brake position and then compared it to the data set - it was as the curve predicted.

I don't believe the curve will ever be a perfect sine wave, what with harmonics, overtones, and the like cluttering up any fundamental frequency.

Since then I have been less rigorous, and I simply re-position the brake until I get the best results.  My Avanti (Daisy) 853 has a brake made from a plastic roller, which doesn't have a lot of mass.  I tune that one with a shaft stop collar.  The Mendoza has a brake/sight base made from a steel pipe nipple.  My Crosman Titan and Crosman G1 both have steel brakes with screw-on end caps that rest against the muzzle.  I tune those with stacks of soda bottle plastic washers between the muzzle and end cap.  All fasten to the barrel with setscrews, and none have threaded adjustment.

In my experience it does make a difference, and is worth doing.  It's probably going to require some experimentation, as I imagine each pellet/velocity/barrel/powerplant combination will be distinct.  My guns also have vinyl tubing barrel sleeves for grip and to prevent blueing erosion.  I have not noticed any improvement in accuracy as a result of the tubing.

The Ruger Mini-14 target models have a harmonic dampener similar to the Browning BOSS.

If you're doing a quantitative analysis of group sizes I might suggest using mean group radius instead of group diameter.  One flyer can make a group diameter measurement unusable, where mean radius kind of "buffers out" the effect.

 

[moorepower]

I would agree. One pellet weight a one velocity for the tuner to see maximum benifit. It may shoot other weight pellets worse than before.

[rsterne]

Interestingly, the rimfire guys use their tuners to compensate for the rather large ES of even target ammo, on the order of 2% over a box of 50.... If you tune the barrel so that the top of the upswing occurs when the slowest bullet exits the muzzle, it is given the highest trajectory.... Faster bullets get there earlier, when the muzzle hasn't quite reached the apex, so start out heading uphill slightly less, but with a slightly flatter trajectory because of the higher velocity.... In this manner, the barrel tuning allows them to reach the target with the least vertical dispersion.... Since we can get our regulated PCPs down to about a 1% ES, even with unweighed, unsorted pellets.... we should be starting with a better potential result.... at least in theory.... If we could get every pellet identical, and shot at the same exact velocity.... in theory a tuner would have no effect, right?.... since the barrel would be in the exact same orientation for every shot....

Changing the velocity noticeably, because of a different pellet weight, or fit, or pressure pulse.... will change where in the barrel whip the pellet exits, and will require retuning, as suggested, of course....

Bob

[moorepower]

Yes, but still "could"/"might" let you tune for a different velocity/weight of pellet.

[rsterne]

Yep, that's the idea of a tuner.... match the barrel to (any) pellet or velocity....

Bob

[Taso1000]

Gerard,

I can't find what are you whacking the barrel with to make it ring?  You mention a wooden mallet later.  Is that what you use?

Are you using this as a rough guide to find where to initially place the weights?  I only ask because a whack from a wood mallet has to send different harmonics versus a firing cycle no?  Or is it the barrel/action/stock that dictates the harmonic only, pellet and velocity remaining the same of course? 

Please excuse my ignorance.  I do remember the spring demonstration in high school physics but I don't remember the math or theory.

Thanks,

Taso

[Gerard]

Sorry to have been less than clear. I've not personally tried hitting barrels to test harmonics/vibration. I was only suggesting clamping a barrel and hitting it (with whatever you have handy to make it ring, such that you get it moving but don't damage the finish) and listening to it ring as perhaps being a useful component in getting a rough idea how the barrel is behaving. A barrel is a metal rod. Sure it has a hole in it, but so what? It's a rod which has particular physical characteristics as regards modulus of elasticity and such, controlling the amplitude and frequency of vibrations particular to its density, length, OD, bore size, any tapering which might be present, muzzle device mass, etc. It's behaving exactly like a tuning fork when struck. It's moving, thanks to a violent impulse. And of course that impulse is different from hitting it from the side, but I'm talking about finding a good starting point from which more refined, delicate variations in mass and/or placement of a weight can then proceed. Otherwise you'd just be taking a wild guess (or W.A.G.) as to how much metal and where to put it.

Clamping it securely at the exact same exit point from the clamping caul (and manner if possible - a pair of semi-cylindrical cauls to enclose the barrel in a vise would be ideal, or just clamp the rifle barrel block itself with barrel mounted if that's practical) as it exits the mount on the rifle simulates the same freedom of vibration as when mounted in the gun, or close enough for getting a ballpark guess going on vibrations. Adding some form of weight at various points and striking the barrel to get it vibrating, one should be able to hear the biggest, sloppiest vibration of the barrel without the weight, then find the placement and amount of weight which most effectively dulls that vibration. Most any material has a natural frequency of vibration. Finding a counterweight which is optimal for interfering with that vibration is likely going to get you close to stopping the barrel's movement during a shot cycle.

Getting into nodal points and peaks of vibration would be great if you had the proper lighting setup and a high speed camera. Analysis of the actual motion of the barrel would greatly enhance your ability to quickly establish the effectiveness of various weights and placements. But of course most of us don't have access to this equipment nor the knowledge of how to use it. So I suggested using your ears to determine how much vibration your weight is damping, finding a minimum value by a bit of trial and error in the vise, then further refining this by shooting groups and making small adjustments to the mass and location of that mass on the barrel.