Load Development for positive compensation - Barrel Tuner?

[williada]

Just noticed a current topic at Benchrest Central is on tuners again. http://benchrest.com/showthread.php?942 ... th-a-Tuner

Do note these guys are mainly short range and there is less insight into the use of tuners at the longs.

[Ben C]

Thanks all for your input.

Tony, got the email and I'm a little clearer on the detail now. Thanks.

David, thank you especially for your comments and knowledge-sharing:

I understood Ben you wanted more emphasis on compensation tuning which is not tuning for the node. If you hit on the right harmonic length your node will be superior and will be enhanced by a compensation tune next to it to broaden the node in a practical sense.

I agree David, now after having more of a look at the methodology and info emailed to me. I will go through the exact process rigorously without a tuner fitted, then depending on the outcome, look at fitting the tuner if I can gain some benefit.

I do need to think hard about my next .308 barrel profile and specs...

Ben...

[John T]

Hello Williada.

We may be acquainted, but I do not know you by your forum name.

My main source of knowledge on rifle barrel vibration and barrel tuners is the article on VarmintAl, the essence of which I have interpreted to be: the slowest bullet must exit before the Top of the muzzle vibration cycle.

After hundreds of rounds, I abandoned my Lambert/Shadetree. My theory is that the aluminum body is too light. Of the tuners I have located on the net, my preference would be the Gene Beggs, even though it does not fool the barrel by having the weight forward of the muzzle.

I do not know who came up with adding Muzzle Mass, but I think it was Marty Lobert. He sweated on his lump, to dampen the muzzle and to constrict expansion of the mouth under heat. Cam threaded his barrel and weight to allow adjustment.

I am told that in the latter part of 2015, Cam was experimenting with a rubber grommet at the muzzle. This jells with a suggestion by Neville Madden a few years ago. I intend to follow their lead.

These are dampeners, not tuners, intended to reduce the amplitude of muzzle vibration.

There is a restriction on diameter, imposed by sighting restrictions, of about 50mm. To my mind, to achieve front-end weight and good dampening, the grommet(s) should be at least 1/3 of barrel length. Should it be a single unit or split into, say, three units? Where should they start, at the muzzle or set back?

Wiliada, your views would be appreciated.

Regards,
John Tracey.
8.3.16

[Matt P]

Here's a photo of the tuners I've been playing with.
There's a hard rubber ring between the inner and outer parts of the tuner, the barrel is threaded and the tuner winds in and out on a 36 TPI thread.
Matt P

[williada]

G’Day John,

Been a hermit for many years now. Yes, Varmint Al certainly got people thinking and shooters are indebted to him and have experimented a little further since he put some of his early work up around year 2000. No doubt he was at it for many years before. Many like him were looking for the ultimate nodal tune at short range through his beam analysis. Alan’s Queens statistics show how important nodal tuning is up to 700 yards.

If you read the American comments on the site I previously posted, one knowledgeable fellow felt beam analysis was not the whole picture. That might be so but Al took people to new heights and probably filled most of the colouring book. He also used the analogy of a guitar string trying to simplify his expression of the harmonics but that is a two end closed vibrational system whereas Purdy highlighted the one end closed vibrational analysis which has greater relevance to free floating barrels. Both considered the multiple orders of vibrations running through a barrel.

The key to the pure nodal tune was finding where these multiple harmonics intersected at a peak or a trough. It is of secondary importance to use metal dampers for muzzle lift or rubber for reflected vibration or overtone dampening. I have briefed Tony in this regard but his lips are sealed. However a muzzle mass does control heat and bore expansion. This is not a problem on cut barrels in practical terms although those skilled in taper lapping are a dying breed.

In order to demystify the concept of the shooting sine wave many commentators have just stuck to a perceived fundamental wave plotted through the centres of groups. Here we see as Al displays the tightest groups have the slow shots exiting at a higher point than fast shots. This is in fact a positive compensation tune for that distance. It is not until you can do incremental load testing as a fine tuning element in .1 grain can you identify the true node and a true node is absolutely velocity dependant. It is necessary for fine accuracy. Past the peak of the sine wave may be sufficient to still group well but it is dependent on how steep the peak is. A flatter peak will give you a broader node and on the left side of that node is the element of positive compensation tune which accounts for a small variation in velocity. Of course the element of positive compensation tune is to right if you are working with a trough.

The old knowledge regarding the compensation tune has slow bullets exiting above fast bullets fits right in with Al’s stuff. But those old skinny, whippy barrels in TR meant the fundamental vibrations dominated the tune and the node was less important because the factory ammo hardly gave a constant velocity. So for the old boy’s, the muzzle weight or movable foresight block was well disguised and was a good option if you didn’t cut the barrel back. Sometimes the additional weight was as small as a shotgun pellet and a grub screw. I reckon a very knowledgeable person in Barry Davies would agree.

Our modern, stiff barrels and hand loading techniques give pretty constant velocity so we can find true nodes easily. The targets are so much smaller. As said before, slow powders and short choppy nodes of modern barrels mean that a heavier muzzle weight is required to control any launch angle to satisfy an element of positive compensation and as such they are a damper and we can use our load development to find a suitable nodal area to explore. Such barrels tend to be more neutral in their compensation profile. We have to rely on lower order vibrations to effect positive compensation if we don’t use the perfect muzzle weight or can adjust it on a thread like Cam did.

However, it is not all that simple because in reality reflected vibrations create stacked waves where outgoing vibration may also encounter incoming vibrations and as said before was an important observation of Mr Long in the development of his optimal charge weight (OCW). These tunes primarily look for groups that are not a reflection of a distorted muzzle but where the barrel is in its straightest position with bullet exit and so in addition mimic a neutral compensation tune and may be suspect at extreme range without tight extreme spreads.

I see the main function of rubber like material used on the barrel or tuner as a damper of overtones and reflected vibrations. I see bloop tube tuners as another way of dampening reflected vibrations and overtones too.

Finding the best node should be foremost in your thinking and that depends on its harmonic length. If its not perfect you can go forward with a bloop tube or you can go backwards by cutting back the barrel or back-boring it. I remember two hot Queens winners, Corbett and Grenness using the same concept of harmonic length, Corbett used a back-bore and Grenness a bloop tube but to the casual onlooker their systems were poles apart.

When I shot with Kaniva, I did use a Beggs tuner for a few years and I fooled the barrel by back-boring it to get the right harmonic length and ran the disks forward of the crown. I used a rubber damper just in front of my fore-end. You can use Purdy’s methods of finding a suitable harmonic length but subtract the values rather than adding tuner length. Much quicker than my trial and error method.

Any tuner should be firmly fixed otherwise they do not transmit the vibrations to be absorbed or fooled. Loose tuners cause grief. May I say that, the aluminium tubes on Pinyon style tuners have to be firmly attached and their effectiveness depends on their harmonic length match. Once that is settled with load development and you are about a node, it doesn’t take much movement to adjust the launch angle with a light thimble. My wife’s tuner replicates this but the thimble is brass. My last tuner is all brass, is brilliant, I keep playing on the lathe. Fundamentally, I use tuner weight at the muzzle to control lift, its length for harmonics and its internal diameter for flack. An adjustable tuner allows you to sneak up on the overlap of the fundamental elements.

I consider that any other weight or rubber dampener that is placed midsection or elsewhere on the barrel is a damper but to be most effective it should be placed on the anti-nodes of the barrel not just say a random third for instance. The anti-nodes can only be determined with proper equipment attached to the barrel – not practical. But I will say, if a bullet starts crooked it will end crooked and it seems logical that a rubber damper closer to the breach to dampen reflected vibrations Long talks about which penetrate the length of the barrel about 7 times before bullet exit is a good thing if it does not interfere with your front rest. Of course the muzzle rubber is a good thing but I think neoprene is too dense to absorb the vibrations. There are so many ways to skin a cat. Just maybe the length of the bloop tube from the crown would be a good indicator of wavelength to apply the use of further rubber rings on an anti-node remembering the harmonic waves are of relative even length the anti-nodes should be starting back midway from the tuner length.

Regards
David.

[Barry Davies]

Hi David,

Yes, all so true. There are many ways to skin the proverbial cat and it's all been done before. The concept of heavy stiff barrels is so ingrained into people's thinking that they ignorantly believe there is no other way achieve tight groups.
I must admit that after many years of " playing around " with barrel tuning I can still be amazed as to what does and what does'nt. But, there are fundamental laws.
I still believe that compensation tuning is the best way to go -- it may mean having two rifles --one for shorts and one for longs -- but the overall achievement is yards better than trying to get one rifle with one load etc to do it all. And relatively whippy barrels are by far easier to tune than heavy stiff ones.

[williada]

Nice tuner Matt.

Barry, if I had unlimited resources, I would use three barrels. Each of these barrels would have twist rates suitable for each section of the trajectory, that is before the overturning moment, the overturning moment and past the overturning moment to optimise yaw and vertical bullet drift as well. Two of these barrels would have the same profile and length and the third barrel would be setup to positively compensate. If it was FO, I would match the first barrel to a flat based bullet and thereafter to a boat tail. Cheers. David.

[macguru]

Perhaps what we need is a combination barrel tuner and 'silencer' !

http://www.smh.com.au/nsw/gun-control-l ... neld3.html

[John T]

A few days ago I read an item which proposed (rather forcefully) that, with a good load in a well constructed rifle, vibration control constitutes the last 1% of accuracy manipulation; 0.1047" at 1000 yards, assuming 1 MOA accuracy.

My conclusion: if the system is performing, it does not need a tuner. If it is not, look to the system's components for solutions, not to a tuner for a panacea.

Barry Davies has alerted us to what I now see as a fundamental error. "The concept of heavy stiff barrels is so ingrained into people's thinking that they ignorantly believe there is no other way (to)achieve tight groups." (On reflection, Barry may have written "..LONG heavy stiff barrels..")

I admit to rejecting barrel makers' advice that a heavy barrel need not be more than 26". No, I wanted 28" and then 30" to get the extra 80 to 100 fps MV.

I will ask my gunsmith to re-chamber a barrel in 7 RSAUM at 26" to test the theory of a 26" heavy barrel at long range F Open.

As for two rifles, it is possible to develop two loads, short and long, for a single barrel in 284 WIN.

John T.
22.3.16

[williada]

John, I agree with your general thoughts, in that a rifle has to be in top shape and constructed well because it skews the harmonic patterns we need to tap into for load development. Whether that be loose screws, poorly fitted barrel, bedding etc or components out of tolerance etc. But its not all about harmonic patterns, it’s about launch angle and yaw too.

A barrel damper or variable tuner is not the panacea for a poor rifle or poor load development and that’s why I do load development without a tuner in the first instance. If it ain’t broke, I do not fix it with a tuner. But I do know that if your rifle is a ¼ minute rifle, not a 1 minute rifle as the assumption you commented on, is based on, a tuner or a muzzle weight will enhance it in the right hands if it has been fitted correctly and the operator knows how to use it.

The comments I have been making have been in the main, responses to other people’s requests and related to stiff barrels because that’s what people have been using in FO; and I agree with Barry, (and we know each other well) and my involvement with barrel manufacture for several years and testing of every conceivable shape and length or paired barrels for testing verification that long skinny barrels work well too. Short barrels work too, as I have mentioned before, the wife’s 25” barrel had a perfect score of 200 out of 200 in TR on day one at Horsham some years back from 300 to 700 yards with members of the SA State Team, the Vic State team and some members of the Australian team present as well as Barry Davies. No-one else had a perfect score, and it was a black barrel too. She only failed to win the two day agg because she plonked one on the wrong target at 900. But although this barrel would hang in at 1000 yards, it was not brilliant. The reason she had a short barrel was for rifle balance given her stature. Rifle balance is very important and particularly for bag handling for scope shooters as well. But 1000 yards requires higher velocity due to different wind zones the projectile has to buck and the downward path of the projectile where there is a tendency for greater yaw influences.

It is one thousand yards, and a trend to incorporate long strings in our competition that will separate competitors and there is an advantage of setting up equipment to be distance specific. Already we are witnessing a Queens series where only one point was dropped in competition in FO, and daily aggs are decided by supercentres. TR shooters are shooting ten centres regularly. It makes sense then to be more discriminatory with more tools at our disposal to get an edge given what the gear is capable of now. One minute rifles do not cut the mustard, quarter minute rifles should be the minimum and the use of a tuner or muzzle weight starts to have an influence here.

I remember vividly Bert Bowden asking me to do barrel testing so his Australian team could gain a statistical edge of ¼ inch or about 1/40 minute on paper, to snick lines based on competitors group sizes which he had examined, with every team member at 1000 yards for a cumulative performance where he thought the international match would be won or lost given the quality of the coaches. It raised my eyebrows! But his point was he only needed a small statistical margin in terms of probability if all things went to plan to win.

In the testing from a machine rest, the better barrels were long barrels due to a velocity edge at one thousand yards. This was factory ammo. In private testing, similar tests have been different where different barrels had individual load development, but what was apparent there was the need to maximise velocity due to aerodynamic yaw factors which are separate influence from vibration at one thousand yards. So I am very wary of assumptions and sample sizes in trying to draw conclusions. What I do know and others are finding anecdotally, that a barrel weight or tuner will improve a good barrel operating in the realm of a ¼ minute rifle, so necessary to have at every distance in top competition as a minimum now.

In light of quality assurance, that comes from unsourced documents, that make statistical analysis which needs to be verified, the assumptions they make, and the sample size of barrels they use, no matter how mathematically inclined they are, I am wary of too. You have to look at the substance and not the language and consider a whole range of factors that are not limited by assumptions otherwise you do not have the big picture.

I am biased toward the British knowledge about long range shooting, because they consistently beat us and the Americans at long range in different disciplines. My feeling is that they know more about compensation theory and the long barrels they use have more peaks and troughs to tap into to get the launch angle right for the perfect compensation tune at long range, i.e. at 1000 yards where matches are won and lost.

Shorter, stiffer barrel tends to throw out a neutral compensation tune and requires heavier muzzle weights to make them responsive if they are not performing, and you have to be really anal with load spreads for long range because crook primers can drop you low with a neutral barrel. As such, I understand why some think a tuner is of little consequence on such a barrel. But it depends where that barrel is going to be used. The low amplitude of the fundamental vibration can work against you at long range if there is a variation of velocity. Hence I feel the assumption was made about 1 MOA for the analysis. That’s huge by today’s standards. These barrels are better suited to 700 yards and results or stiff setups are seen in Alan’s statistics at long range for Queen’s events.

The point I make, is that while paraphrased vibrational analysis of the author shows a tuner is a small influence, the weight of the tuner can be adjusted to determine the launch angle in a desired vibrational range necessary for a positive compensation tune which gives a relief to small velocity changes. It is this effect that the analysis does not cover. If you use a nodal tune it is velocity dependent. If you use an OCW tune, you are getting reflected vibrations that could be reduced by having a barrel length determined by its harmonic length or using a tuner forward of the muzzle to take the chatter of reflected vibration to a false wavelength determined by the end of the tuner. Because the fundamental vibration is of roughly equal wave segments, the crown is on the same wavelength for the bullet to escape chatter free and the tuner also on the same wavelength cops the chatter and it doesn’t matter because the bullet is gone.

It is very apparent higher velocities mattered at the Brisbane Queens last year at one thousand yards with the 7mm’s. A longer barrel does add significantly to velocity. One of the members conducting the “Train the Trainer Program”, specifically re-visited this with tests of different known nodes at 1000 yards. This was considering the gyroscopic stability and the yaw factors which influence group size. The results were as predicted.

I also add that the many test sheets I have been reviewing since 2014 of FO shooters around the country, following the “Train the Trainer” program principles, suggest the mid range load and the long range load for the same barrel is mostly not possible or optimum as barrels tend have a personality of their own.

May I conclude by saying that a weakness of the long skinny barrels is found out in long strings at 1000 yards as they heat up. Despite heat treatment, the harmonic length will vary as do bore dimensions with expansion. A heavier barrel is more heat stable or a barrel weight added to the muzzle end can perform a similar function. Hence a compromise in barrel profile of a barrel not too heavy and not too light but long of straight taper is more desirable for 1000 yards.

A lot of the argument boils down what distance, how many shots, what type of tune, and yaw factors for long range. David.

[plumbs7]

Just posting to put this back at the top for revision! Great reading !

The more I think I know ......the more I know that I don't know !
I still have a long way to go !!! Great reading again !

[johnk]

May I conclude by saying that a weakness of the long skinny barrels is found out in long strings at 1000 yards as they heat up. Despite heat treatment, the harmonic length will vary as do bore dimensions with expansion. A heavier barrel is more heat stable or a barrel weight added to the muzzle end can perform a similar function.

Wish Nev Madden still made his barrels with the fine threaded finish like he did at the beginning. Those barrels offered the best part of twice the surface area to dissipate heat than today's "fancy finish" one does. I reckon that aided their shootability.