Tuner?

[williada]

I recently sent Danny some thoughts about tuners he requested. Seeing I have had a few people ask me about them, I decided to post some information again for others who may be interested and added a bit to comments I gave to Danny. People may have different ideas and they are welcome to contribute their experiences. You don’t need a tuner if you get load development right but they can assist in other situations.

There is a vibration moment as the bullet leaves the muzzle and that is why I have the effective weight of my tuner past the muzzle rather than just a weight on the muzzle. I prefer a variable tuner. Some of this discussion has been had before in relation to a fundamental weight that counters fundamental barrel movement and a lighter weight which acts on barrel pulses. So I don’t intend to elaborate on these characteristics in any detail. If you have a heavy profile barrel, the tuner weight tends to be heavier.

Remarks to Danny.

Making the tuner out of stainless is fine. If you can’t thread your barrel to attach a tuner directly, (so you can clean your muzzle/crown), have someone slip on a threaded band (sleeve) and “Locktight” it in place to receive the inner tube of the tuner. Make sure it is flush with the muzzle. Any loose tuner is bad news. Also make sure the internal section or tube butts up hard against the end of the muzzle, so that the desired internal diameter starts immediately from the muzzle. For a projectile of .243” (6 mm) this diameter is about .7”. For a projectile say .308”, the internal diameter is about .86” and in the case of your old tuner .88” which is fine for 30 calibre. You can always run with .7 for your Dasher and if not right, you can open it up. For others who use 7mm I calculated the bore diameter to be about .79” for the tuner inner tube. For .223, about .62”. I put a neoprene washer under the lip of the thimble, to make sure the thimble is vibration free. I also put a grub screw in the thimble to lock it in place as well.

Sometimes the weight of the tuner you are going to make is not sufficient to make it a fundamental weight, for fundamental lift tuning. You can try to induce about an 80 fps difference in test rounds with different loads and try and hit the same spot at twenty five yards by altering barrel lift by adding weights to a thin aluminium bloop tube to come up with a fundamental weight. Then you go about making a thimble to replace the weights you added of the same weight to allow for fine adjustment later. If you are getting one hole with little additional weight, then load development without a tuner will be enough. If its a tad enlarged, then you will only need a light tuner.

Its another ball game if you can’t make the shots impact in a suitable position at twenty five yards i.e. with slow bullets impacting on top of fast bullets for a positive compensation tune or about the same elevation for a neutral tune. This is often the case with heavy profile short barrels. So take your testing distance to 140 yards using loads you would for normal load development. It doesn’t really matter because you can still work on secondary and tertiary vibrations with a lighter tuner and not worry about a fundamental weight. But the exact weight involves a bit of guess work. The lighter weight with a variable external thimble acting on secondary and tertiary pulses can still tune for group shape before or about a node in relation to either a nodal tune, an OCW tune or a positive compensation tune – whatever your poison. Anywhere between 2 - 6 ounces is fine. Its a bit of suck it and see, so make a few thimbles of varying weight up and see how responsive your gear is to varying each thimble. Any weight will act as a damper and possibly extend that node if you are a nodal tuner. But I really hunt for an OCW tune about a positive peak where possible.

On my wife’s rifle I have gone for an inner tube made of aluminium so that the actual thimble of the tuner which is made of brass (1” long x ¼” deep), moves forward and aft along a thread. It happens to work best with the thimble weight balance just past the muzzle. You could make this thimble deeper for more weight on a heavy profile barrel, not a light one like hers. You can make your internal tuner tube longer to gain leverage if you think the weight is insufficient. The purpose of this design is to focus the weight on the thimble and not the internal tube which it moves along. It makes the barrel a little more responsive to change. Similar to the Beggs tuner which has two (approximately) ¼ “ x 1 ½ “ disks locked together covering half an inch of inner support tube therefore focussing the weight on a narrow section of the tuner rather than on a long length. This is working on a leverage principle rather than a total weight principle to equalize forces such as used with just a large weight on the muzzle as a damper.

Basic Tuning

It really does not take much distance to move a tuner between nodal pulses. The worst thing you can do is try and chase shots with a tuner. Its setting is fixed and based on predetermined tests like I do in laying out load development plots in the horizontal as I have done with Tony on a previous thread. A lot of people don’t realize that in using a tuner they are actually moving from a peak to a trough node if they go far enough. There is confusion between what the consider to be an upper node. I think they are really meaning the next node. So any direction, forward or back you actually move between a node. My preference is for the positive peak so I like to skip the next node because it is a trough and go to the next one again knowing it will be a peak. If I am getting too much vertical I move the tuner out, to make it harder for the barrel to be whipped up too far, and if I am getting lateral, I move the tuner in. But this is basic use.

In advanced tuning, I tune the rifle without the tuner in place for my best tune, keeping a track horizontally in a round robin test of vertical spreads. I then attach the tuner, and with further testing of the selected load, move the tuner to hit the same spot as my best load in elevation. I then fiddle fore and aft altering it changing the group shape with a bit of vertical in it to maximise the compensation tune I had already established.

This is not a nodal tune, which you can work up with load development with the tuner in place from the beginning which is most effective from 300 to 700 yards.

I then lock my tuner in place and don’t touch it unless there is a clear change in atmospheric density. Then I only move the tuner 1/3 to ½ turn at best because there is usually something else responsible for errant groups.

A major purpose of my method is to have the tuner respond to conditions as if I was making a change in powder based on past testing and experience in changed conditions. For example in the old days, the tune difference between Gippsland and Bendigo was in the order of .6 grain in .308. In other words 46 grains of 2208 for Bendigo with a lower atmospheric density to 46.3/46.6 for various Gippsland ranges with higher atmospheric density. The other major purpose is of course to maintain a group shape that is less sensitive to the wind with that element of vertical in it, but not too much to tip you out.

If you were really serious about a Queens etc, you would conduct tuning at the venue and not try and second guess it, unless you have vast experience. A tuner is not for a beginner, as you have to understand the theory behind its movements for various tune methods such as a nodal tune, an OCW tune and a compensation tune and at what distances and in what atmospheric conditions it is appropriate to use each method of tune.

Only with testing do I make larger changes with my tuner to cater for a change in mound angle which will change bore angle at long range. I do this testing by altering the height of my aiming point at short range to mimic mound angle changes that I can expect at different ranges. You need to keep records of mound to target angles on different ranges if you want to go down this path. Its a bit over the top but doable.

So the normal length of your inner tube does not have to be that long, but I would be going with a minimum of 1.5 inches past the muzzle even though the thimble weight close to the muzzle often works best. But if you want to accommodate more leverage to cover mound changes then you could run to 4 inches. It is far easier to adjust your front rest head angle like Alan and I have for mound changes (but really only for long range compensation tuning).

When I first test with my tuner on, I place the rear of the thimble where the muzzle ends and move forward from there. Because the barrel moves up and down you will find a spot that suits because the patterns tend to be rhythmic.

You do not want a tuner that makes the balance too front heavy. Lighter but longer inner tube will work. But you can keep making the tuner heavier to maximise rifle weight, but only if the balance is right and assuming you have not gone past the fundamental weight for a tuner. On the other hand you may want a light tuner to maximise barrel lift for a compensation tune but where it can influence group shape to make your gear less wind sensitive or in the case of a compensation tune allow slow bullets to impact higher than fast bullets. So the best tuners are really custom tuners. This development takes a lot of time. So if you have a campaign in mind for a set event, you have to work up to it and prior planning prevents piss poor performance. Otherwise set and forget your tuner based on the best group shape from your round robin testing.

I don’t use marks for reference, because you find your sweet spot first. I use the grub screw as the reference point and go in 1/3 to ½ turns or weeny bits knowing a full turn only moves you .004” anyway depending on your thread pitch. The pressures on bullet exit are immense and you don’t see fighter jet planes with big wings, so only a small about of trim is necessary about the sweet spot.

Hope this can help you Danny.

[williada]

Just noticed those fine looking Begg's style tuners on those US rifles, particularly Speedy's, and those mirage shields on Tony's advertisement in the For Sale section.

Geez Tony, I know the renaissance painter Titian was a Venetian, but that colour scheme you got painted would have my eyes bouncing more than the mirage on the venetian you're getting cut down. Can you get them in plain green? David.

[DannyS]

Haha David, I also noticed those tuners, good way to bump up this subject.

Cheers
Danny

[Cameron Mc]

Something to ponder with regard to Tuners.
Lot's of thoughts and theories on ths subject.

http://varmintal.com/atune.htm

Cam

[RDavies]

Just noticed those fine looking Begg's style tuners on those US rifles, particularly Speedy's, and those mirage shields on Tony's advertisement in the For Sale section.

Geez Tony, I know the renaissance painter Titian was a Venetian, but that colour scheme you got painted would have my eyes bouncing more than the mirage on the venetian you're getting cut down. Can you get them in plain green? David.

Any pictures?

[Razer]

Pictures are here;
Need sunglasses before opening.
http://ozfclass.com/phpbb/viewtopic.php?f=6&t=6537

[williada]

Good work Cam and Ray. Theory is correct Tony, but those colours!

[ecomeat]

Good work Cam and Ray. Theory is correct Tony, but those colours!

I wish Alan had that single finger (the bird) smilie that get used a lot on one other gun forum
I understand how you Victorians wouldn't quite grasp the passion behind State of Origin rugby league, as it really is just a Qld V NSW thing, but the passion is rather intense around game time. I could just add that for me (lots of us up here in Gxds country, actually) Qld flogging the a##e off NSW in a game or a series is nearly as good a feeling as shooting a possible, with lots of X's
As for the shields, the subject of this blasphemous ridicule ....she can do basically anything, and would even have a green suited to Victoria !
Now David, stop hijacking your own thread .

Re Tuners...the subject here.....David have you seen the very slim one that Eric Cortina (Team Lapua man in the US, who accidentally started the 89 page long thread on Long Range Tuning at 100 yards) makes and sells in the USA. I am sure read it somewhere that they basically don't add any weight , but rather just move the small weight in or out by adjustment. I will find a photo if you haven't seen it before. I can remember looking at the photo of his slick little unit, and wondering how it could work well, given some of the larger ones I have seen in Australia
Tony

[ecomeat]

The photo of Eric Cortina's tuner is just down page 1 of this thread
http://forum.accurateshooter.com/index. ... =3828708.0.

[DannyS]

Thanks Tony, nice looking unit.

Cheers
Danny

[williada]

Hi Tony, I have seen Eric’s style of tuner before. Its probably held in place with neoprene washers under the thimble? The weight of the tuner depends on the how responsive to tune your barrel is. It appears that Rod and Alan are going to try the 34 inch job that I am sure Peter and Dave would love to see the data with respect to positive compensation. In that situation, in a long flippy barrel, I would go with a light tuner to work on group shape about a positive peak based on load development.

If you look at Cam’s reference to Varmint Al’s site you can see where the untuned barrel is dampened without much bore angle variation which we may still require for 1000 yard plus. So tuner weight is a big factor. In the latter scenario, we used to use grub screws and shotgun pellets, so positioned, (like a wheel weight) to counter a little barrel torque or secondary/tertiary vibrations in lift or both. You will also notice Varmint Al says the sweet spot is just before the positive peak. That’s a micro look at positive compensation.

I have used all sorts of tuners, they all work, but I have had excellent results with the ones going forward of the muzzle using Obermeyer’s theory, to condition the atmosphere behind a boat tail as it exits the muzzle in mitigate against gas and particles upsetting the projectile. (This is not so much an issue with flat based bullets and short range shooting). He worked on changing the internal diameters of the bloop tube to get best efficiency. The bloop tube in fullbore increases sight radius.
The bloop tube can also perform the function of a tuner, so why not get its weight right too or thread it 28 or 32 tpi and attach a variable thimble to it.

The tuners finishing at the muzzle do not take into account another vibration factor just on bullet exit. If you can imagine the stream of gas behind the bullet still pushing it forward, then you can imagine this stream of gas varying thrust angle with vibration movement as the bullet is suddenly released. Its analogous to defecating into a pan. Cheers, David.

[DannyS]

Interesting analogy David, but probably quite apt.


Cheers
Danny

[Norm]

Very interesting subject. It gets the thought processes going.
My first attempt at simply adding a weight to my barrel sure worked and I am sure that it could make even further improvements to my accuracy if it was the right weight and could be adjusted for position. Something to play with and work on.

David, your thoughts on muzzle gas exit effects on the projectile. This brings into question the muzzle crown shape and angle.
Also wondering how the muzzle brakes that are common on 1000 yard benchrest rifles go in this regard? They are neither a tuner or a traditional target crown yet they must do the job to be so popular in such a demanding sport.

[williada]

Norm, gas leakage to one side of the projectile while the other side is still bearing on the barrel will skew the projectile off at an angle. That is what a crook crown does. Given that velocities vary, so will the angle of departure as separate from the barrel sighting plane, barrel lift, barrel torque and vibration. So it is critical with a ninety degree crown or a modern target crown of 11 degrees that these angles are maintained across the face of the muzzle for an initial even blast pattern perpendicular to the bore.

However, due to damage of the crown by cleaning rods or dropping your rifle on its muzzle, I have a small bevel to allow the cleaning rod to self centre when it’s drawn back with a brass wire brush attached. The mark of a competent smith is to also have the groove at the crown at six o’clock to save wear on the rifling from the cleaning rod as it pokes through. The bevel can range from 45-60 degrees, it doesn’t really matter. In bench testing, I could not pick any group differences, but that was a long time ago with factory ammo. You can also grind a bevel with a ball and cutting paste and this will always guarantee the crown bevel will be perpendicular to the bore. I preferred to use a sharp cobalt or high speed tool bit on the lathe rather than a tungsten bit for which you need to run the lathe faster unless you want to chew steel, cutting from inside to outside. You can also get a small hand tool from Brownells with a pilot (or you can make your own pilot for a different calibre) to nip up the bevel. Some do this about every 500 rounds.

A good crown will always show an even star pattern about the rifling on the muzzle face where carbon builds. An uneven pattern can also indicate variance in land height and or width. A smudged pattern indicates the crown is not cut perpendicular to the bore. Both normally remedied by cutting back the barrel and making sure the crown is placed at the minimum bore diameter. So it is necessary to be able to remove the tuner to inspect and clean your crown.

From bench testing, I could not see any real difference between the 90 degree crown and the 11 degree crown of the general muzzle face - again, testing with factory rounds, a long time ago. Yet we are told the 11 degree crown works better with boat tails. Any plumber can tell you that a gas torch has a 12 degree cone to focus the heat of the gas to a central point. Maybe that is what a 12 degree cone could do on the rear of the boat tail bullet and so centralising its thrust to reduce yaw on bullet exit. Shoot at night and you may well see flame. Maybe the minor merits of this, together with the Obermyer tube which is said to, in addition, condition the atmosphere, assists with bullet stability.

As we are not permitted to use muzzle brakes, I have never gone down that path to consider their strengths and weaknesses with gas control and related accuracy. Yet I do know that shooters in the past tried gas bleed ports to stabilize pressure closer to the breach to take out pressure spikes. Also having worked with a few of our service personnel a long time ago, the auto weapons were tickled up in the gas control department to assist with accuracy. I think just about everything has been tried and now we are into marginal benefits that are wiped off by a puff of wind or a burst of sunshine. David.

[williada]

The following targets might be useful. I use the first one at 25 yards for setting wind zero and elevation with the .308 155 grain and the second one at 140 yards for Round Robin load development . The second target has to be scaled up a bit so that the graduations are in minutes at 140 yards. It’s currently set at 120 yards for minute of angle.

I use the second target again once I have settled on a load without the tuner on. I then put the tuner on and see if I can get the tuner to hit the first best tune elevation and fiddle with it a bit for group shape and tighness. Just like with powder, you can then match tuner spreads to nodes or positions that are equivalent to powder changes.

Fig 1. 25 Yard Target


Fig. 2 Load Development Target