Load Development for positive compensation - Barrel Tuner?

[Ben C]

OK, In recent years I have just been shooting at club level only. As some of you may be aware, I used to shoot competitively a few years ago with some success. With increasing family/work/financial commitments, I've had to back-off from competitive shooting for a while, but still love to shoot most weekends at either North Arm, Kilkivan or Fraser Coast ranges. I am in the process of having a new .223 Bartlein barrel fitted to one of my F-Class rifles. It's specs are:
32" Heavy Palma profile, 5R rifling, 1:7 twist. Also having the last 35mm of the barrel turned to 22mm for a Davies (adjustable) tuner to be fitted. I am intending to run moly-coated Berger 80 gr VLD's (Lapua brass, 2208 powder).

I haven't bought a new barrel for a few years, so I am interested in trying a different approach to load development than I have used previously. I have had some good results with my 'usual' method, but have had issues with vertical (and other mysteries) at the longs. My usual method has been doing 5-shot groups with different powder charges and bullet jumps/jams until I find a load that 'groups the tightest', which is then the load I use at all ranges. Now probably realising that this isn't ideal load development method for the longs.

I have been reading with great interest some posts about 'positive compensation' and 'barrel tuners' and reading groups that are shot in round-robin with no scope-adjustments through the various groups. Fully aware of the need to have accurate velocity readings during load development, I have also recently purchased an accurate chronograph (Oehler 35P with 8 foot bar, which in theory, gives accuracy of less than 2 F/s at 3000 F/s projectile speeds). I went for the Oehler over a Magnetospeed because I don't want anything hanging off the barrel to interfere with barrel harmonics during testing.

I have been able to grasp the general concept of positive compensation and barrel tuners, but I am still a little unclear on 'exactly' where to start and why. I have the idea that I can find a good tight-grouping load for up to about 500 yards, then be able to use the tuner to 'positively compensate' for ranges greater than 500 yards. If I know what effect the tuner variation has on the different velocity projectiles, I'm thinking that through trial and error (whilst shooting through a chronograph to see what respective velocities the high and low shots are doing), I will be able to determine the 'best' tuner setting for each range - which could then be used in future. Open to comment on this strategy.

Question here for Williada and others who are in the know:
- Do I do initial load development without the tuner fitted, then fine tune those loads with the tuner installed?
- Can you re-cap on the exact method for shooting 'load development' groups (or point me to the correct thread as I can't seem to find it).
- The process of selecting the best load (based on the groups shot)?
- How to adjust the tuner. I have read that when vertical begins to appear at the longer ranges, adjust the tuner towards the action, which may have the same effect as varying the powder charge. Is this correct?
- Any other advice you can offer to assist would be greatly appreciated.

Thanks in advance.

Ben...

[williada]

NB I have made a few edits for clarification.

Hi Ben,

The real value of positive compensation is better suited to bigger calibres but the .223 is fantastic up to 700 yards. Unfortunately the BC decays rapidly in .223 and the other issue is one of yaw due to the lack radial torque to buck unstable conditions over steep mounds which is related to the diameter of the projectile. Although your 1-7 twist may counteract this. However, using an 80 grain projectile with this twist will increase your bullet spin drift. With switching frontals there will be more vertical than with a slower twist. Left wind lowers and right raises so don’t get confused with apparent vertical. This is not a tune problem. Your Bartlein barrel on the other hand may well give you higher velocities to offset BC issues being a 5R. Generally, I would look to a bigger calibre for 8, 9 and 1000 yards unless conditions are benign.

No amount of positive compensation can offset poorer BC, Yaw factors and drift factors. Its just part of the mix.

The Davies Tuner is a great tuner, and yes by moving it fore and aft you can change the launch angle of the projectile for compensation at each range while keeping the velocity in a constant range. However you have to be aware that any velocity change due to changes in atmospheric density outside the compensation spread of velocities puts you well away from a node. The compensation tune is just the left of the true nodal tune which is at the peak on a sine wave. You must also be aware that a true nodal tune depends on the harmonic length of a barrel.

I cannot go into details here because I gave an undertaking that I would train the trainer and they would follow up with a program for other shooters through word of mouth. Someone may contact you Ben, as a few have been using my general approach in QLD, some the intermediate level, but not the advanced processes as that demands a lot of ballistic backgrounding. Due to health issues, I cannot do it all and there have been a few requests. It just takes so long to write it all up and I get too tired on an individual basis to bring all people up to speed as their knowledge base is so varied.

That being said, I am currently shooting a .223 due to supply issues and I have a number of components that need to be used up. At the shorter ranges it is as good as anything out there. I did do a primer test before load development and am running with cci 450’s 25 grains 2208 with 80 grain Sierra’s. Each barrel is different, so do the testing.

You also have to trade off the relative size of your compensation group compared to a nodal group or an Optimum Charge Weight tune. That means you could be better off with an OCW tune if it is very tight than a looser compensation tune running into a nodal tune. It depends on what your barrel produces or what components you have to vary. OCW tunes mimic neutral compensation and if its tight the odd low velocity shot may still hang in at 6 o’clock. You have to know the difference between these tunes and in what circumstance each type of tune will be best for you. It is not as simple as I want a positive compensation tune and sometimes we have to settle for the next best alternative if your gear is not capable of producing the tune you want.

I do all my testing in the first instance to see what the barrel is capable of without a weight or tuner. If it shoots fine I don’t add the tuner (and the launch angle is right where I want it too). Then again, I include the tuner in the harmonic length for the right nodal group if I have to. Not all off the shelf tuners are actually suited to the true harmonic length of your barrel, that’s why they have to be custom jobs but the variable ones will impact on the launch angle even if they are not the tightest of groups to bring you closer to the mark.

Once you find a good group amongst your plots of at least 5 shots per group and it is near a peak, put the tuner on and see if you can adjust it to hit a similar elevation. Sometimes it can't be achieved. It means you have to adjust for another harmonic length in the oscillation cycle by lengthening or shortening the bloop tube and then adjusting thimble weight for the correct degree of lift. It is time consuming. Generally speaking, this is where a charge weight matches the launch angle of the tuner. Having found that, move it in ¼ turns and observe what happens to your groups.

On the other hand put the tuner on before load development commences but leave it in a fixed position. After you have done the load development move your tuner out in quarter turns from the muzzle outwards and see what happens to groups as the next best alternative IMO. The quality of your groups is determined by harmonic length and so your charge weight is most influential here. The launch angle is more influenced by the muzzle weight. When it comes down to adjusting seating depth in fine tuning, you are in fact playing with compensation both in bullet exit timing and finding variable charges that actually sit in a compensation range. This is indicated by the relative sameness of elevation of groups irrespective of their size. Groups tend to hold their shape with distance albeit they may enlarge. Remember the charge weight determines both launch angle and velocity for tune. If the atmosphere changes velocity you can only play with launch angle. Changing the launch angle by moving your tuner does not substitute for group size from an harmonic perspective but it may compensate a bit to give you some leeway if it is not outside the compensation velocity spread.

My tuners start forward of the muzzle, so I can’t speak for others. Purely from a compensation perspective and not for an harmonic tune, then moving the tuner thimble out reduces barrel lift. I apply this to compensation vertical. I move in with too much lateral. There are some overlapping effects on the node too and there is a node before you and one behind you. This movement can be the opposite to the compensation tune depending on the tighter node and due to increased velocity due to atmospheric conditions where you fall off the node. In such a case you can wind back because you have gone past both the compensation point which sits to the left of the node and the node point. If velocity decreases the compensation point picks you up because it is to the left of the node. Usually an OCW tune demands forward movement with vertical. But it depends on whether velocity is increasing or decreasing. So where you want to be also depends on what node you want in the oscillation cycle. This means you must study your test groups and the group shape will tell you whether to move forwards or back. The other thing that occurs is barrel growth with heat and heat dampens vibration. This really affects the harmonic length and group size. Start your testing with four warm-up shots. It is so complex for the beginner it is better to set on your best group or use a large mass tuner.

The commercial ballistic programs do not account for positive compensation. They do a fine job simulating with SD’s but assume a constant launch angle. You have to simulate true compensation intersections in Excel by varying launch angles in minutes not degrees at a set distance if you want to visualise the compensation effects at that distance or do it by trial and error. Its easier to have a mildly compensating rifle close to a node determined at 140 yards unless you know what to expect.

David.

[DenisA]

Hi David,

When we talk about tuning a load, we're always looking to use the peak of the positive sine wave and the "on ramp" to that for positive compensation.
Is there any reason why we can't or shouldn't use the trough of a negative sine and the "off ramp" for positive compensation?

[williada]

Ah Denis, you’re moving to the intermediate class level. The reason I did not mention this, is I did not want to confuse beginners with too many scenarios and they would be totally lost with a variable tuner and which way to move it.

Yes, the trough is a point to use and sometimes they can be super tight and it is an area where we can tap into as the barrel changes direction again. But on a trough, we look to find the compensation tune to the right of the node. We are then tapping into a rising barrel. The positive compensation tune must always be on a rising barrel. The fast shots get out low and the slow shots are tossed higher. If I remember correctly, Craig had one such barrel which put in solid performances.

But there are often a series of nodes to tap into. Its generally a good idea to look at the highest peak or the lowest trough in a trend for starters to maximise swings with choppy nodes with slow burning powders. These maybe the tightest nodal areas, but sometimes they are not and other areas might be more prospective for particular distances. You then apply the theory of the second best or next best alternative.

You have more chance as the real heat increases velocity if you can move from a nodal tune to a compensation tune on a trough assuming you did your nodal testing when it was cooler and the nodes are choppy. Some people see these areas as broad nodes. They are not. You are slipping from one tune into another and maintaining the same general impact with the shot.

It is a safer bet to use a positive peak if you do not understand all the combinations of tunes because on a negative trend of troughs there is not much insurance as environmental changes can put you quickly into negative compensation if velocities fall; whereas on a positive trend, the barrel tends to slip into a neutral compensation profile which is still redeemable with good hand loads at long range.

But hey, Formula 1 is always raced on the edge and they need to change tyres for the road conditions.

[plumbs7]

Hi David , u have seen my combination fixed weight or Harmonic dampener ! One thing I found since I've had the weight on the muzzle . Is that when I now put my mag speed on the poi des not change at all. It used to shoot high about half a minute ! Is this a good thing or have I taken out all of the harmonics ? Another thing was last year At Northarm I had terrible vertical . I put the weight on and the problem went . Shot well at Warwick except when I moved the middle o rings forward of the middle so my Sons gun would clear the stop. I had horrible elevation until the next round I moved it back and hey presto was on song again. I later found that my front scope mounts were loose ( doh!)

Was the harmonics that non existant that it didn't bother the scope mount situation when I moved the middle o rings back to the old position? I don't know !

Of late it has returned good waterline and seems to be in tune ( owner isn't ! But working on it !)

I guess I'll ask the question again ! Have I taken too much harmonics out? .........I guess the target will tell the story!

Oh , all so is dampeners better or tuners?
Regards Graham.

[Ben C]

David, thank you for your detailed response. Greatly appreciated.

FYI - the .223 rifle I am re-barrelling will be used primarily for ranges up to 500 metres. It is actually built on a Manners T4A stock with a repeating action built primarily for use in 'Combined Services' and 'Practical' type shooting events. Me, being (mostly) an F-Std shooter, I also have a .308 target rifle (Kelbly 1M stock with Nesika K action, Maddco 28" 1:13 heavy barrel (currently)), I will be looking at re-barrelling it in the not too distant future. So, I thought I have a play with a tuner (on my .223) to try and get a grasp of the best way to use the tuner and to determine improvement possibilities, particularly grouping at longer range. Point taken regarding the range-distance limitations of the .223 though.

From here, I will do some load development at 140 Yards (with and without the tuner) as you have suggested. This won't be for at least a couple of weeks or so as the gunsmith is still yet to fit the newly arrived barrel. I'll see how things go.

David, regarding your comment:

The Davies Tuner is a great tuner, and yes by moving it fore and aft you can change the launch angle of the projectile for compensation at each range while keeping the velocity in a constant range. However you have to be aware that any velocity change due to changes in atmospheric density outside the compensation spread of velocities puts you well away from a node. The compensation tune is just the left of the true nodal tune which is at the peak on a sine wave. You must also be aware that a true nodal tune depends on the harmonic length of a barrel.

I would have thought that the tuner would perform two main functions, that is, as you have said moving it for and aft will change the launch angle, but wouldn't it also 'slow' the barrel vibration (whipping movement) on the vertical plane due to it's added weight placed at the end of the barrel? (Physics principle). This would in turn 'lengthen' the nodes?? With lengthened nodes, you have more 'room' before the load/barrel combination goes out of tune. A greater mass 'tuner' or 'dampener' would have this effect even more so. I'm quite interested is further understanding the dynamics a play here, as I'm trying to work out an optimal replacement barrel for the longs with my .308. Considering a long (32" or 34") with a heavy-ish tuner at the end of the barrel. The idea is based on the principles mentioned above, and that the long length barrel will give higher velocities - which is also beneficial for F-Std at the longs. This might also allow use the trough of a negative sine and the "off ramp" for positive compensation? Which may give tighter groups?

Open for further comments please David...

By the way, why don't you retire to the Sunshine Coast of Qld...

[williada]

I need to clarify testing at 500 yards for Ben. If you want a positive compensation tune, then you want a load that is sufficient to hold in at 500 yards and not be super tight in elevation terms because this is the approaching a middle distance of trajectory where compensation spreads are going to be greatest if you want the rifle to compensate at long range assuming you can identify the slow shots are going high.

If the group is super tight at 500 it may be compensating at that range and past that you enter a brief area of neutral compensation which drops off with greater elevation impact into negative compensation at long range.

If the tight group at 500 yards is a nodal tune it will remain tight if velocity has consistent low extreme spreads. But you run the risk of falling off the node should the atmosphere vary velocity.

I only use 500 yards to confirm 140 yard testing.

You may identify a starting point with incremental loads over a chronograph, plot these and prospect the flat spots in load development having done a primer test first with a safe pet load.



Graham, the target always tells the story. There are too many variables to draw a real conclusion. But I might say, some people clasp the scope with one mount and bed the second set to prevent a further source of vibration impacting mainly on the secondary and tertiary vibrations we fine tune with. It has less impact on the fundamental lift. It may be one set was doing all the work. I would say your quality reloads kept you out of trouble and the barrel was doing the same thing. Just luck and coincidence. But there would be differences with the fall of the shots over a greater range of distances with your magneto speed leading to a difference in group size. Yes, your rubber rings have to be placed at the maximum amplitude of vibration to dampen it more efficiently.

A variable tuner is a dampener with more options. A variable tuner can be as heavy as your mass dampener. The mass dampener works with the fundamental wave and the tuner of equivalent weight can adjust for further harmonic overtones. But ideally they should be matched to the harmonic length of the fundamental wave.




Once upon a time there was a cow munching fresh clover. Bees liked it too. In her bliss, with her eyes closed the cow was happily munching the clover and swallowed a bee. The bee was so irate he was about to bite the cow but was overcome by the mellow warmth of the cow’s mouth. He thought to himself, I will have a nap first then bite the cow. When the bee woke, the cow was gone.

[macguru]

Do you find any of this makes an actual difference to your scores ?



Just asking ....

[plumbs7]

Do you find any of this makes an actual difference to your scores ?



Just asking ....

Hi Andrew , good Question ! I've seen rifles without mass dampeners do well . Just at crows nest the top shooters were naked and without knobs! ( a private joke in Se Qld about knobs! ) certainly my best score to date is with my Rem .308 shot at Wandai opm 60.8 at 500 yds. This was a naked barrel! 1000 yds win at Nats was a naked Barrel and that thing was a laser ! But had huge vertical at 900 yds . Would a mass dampener may have helped counter that? I don't know . I suspect that vertical was caused by leaving powder in the hopper while loading over a number days. Since learnt that this is a big no no!

I was privileged to have master in my club and he really was the first one that started using mass dampeners ! His guns were always in tune and both of his guns top scored in 2013 . He was also a master pilot and frankly I don't think we will see anything like Cam again! He Believed in it and it worked for him and I saw it with my own eyes !
Unfortunately I'm not Cam and still very much a work in progress !
I'll finish by saying spending the 3-1/2 years with the Master ( he hated me calling him that lol!) was priceless and I believe it does make a diff , but my skills aren't yet matured like Cam's to make the most of it! Rest assured , I am trying ! Natural Talent only gets one so far , the rest is just plain hard work! Something I've been able to bluff my way through till now ; having to come to terms with a Moa scope! I'm sorry for blabbing on !
Getting sentimental , sorry!

[DenisA]

David, thanks again for your in depth explanations and teachings. Yours is a selfless and priceless contribution of knowledge that would otherwise leave people like me un-aware. I'm confident that your input has and will continue to make me a better F-class player.

Do you find any of this makes an actual difference to your scores ?



Just asking ....

It's become a common trend in F-class, especially Open with its high X counts, for competitions to be won on X counts with very few, if any whole points dropped. Saving some missed X's on the vertical plane seems like an obvious place to start improving. Nothings more frustrating than a 6 where the X'ring might have corners or even a 6 anywhere inline vertically with the X ring. Aim small miss small.

[williada]

Thanks Dennis for your kind words.

Ben what you say is correct and there is an overlap of the functions as I said, but it is the relative magnitude of the effects that is important. In order to analyse this I chose to focus on the independence of the functions rather than the union of the forces as could be illustrated by a Venn Diagram to keep it at a basic level.

There are lots of influences on the fundamental barrel lift which is a primary goal to control such as stock centre of gravity in relation to bore line, fulcrum points, barrel weight and stiffness. FO barrels tend to use slow burning powders which tend to have choppy sine waves and in practice you are tapping into secondary and tertiary harmonics or you need a bloody heavy mass damper to harmonise the fundamental vibration at the muzzle. This may affect bag handling.

Plumbs, I suspect Cam knew how much weight to add to his mass damper and matched this to the powder charge which excited his barrel lift and overtones. No doubt he was a master wind reader and could handle a larger group when conditions changed his velocity. You were blessed to have so much time with him.

The other way is to trick the barrel into thinking it is longer by adding a tube forward of the muzzle of the right length to match the best harmonic length for the tight groups. To this, I add a thimble, which I find requires tiny movements to adjust launch angle once I find the spot which is a trade-off between a harmonic node and a compensation point. So what you say is correct, but it is really an art not a science due to so many variables. On the other hand, lighter FS barrels are more responsive.

I have found that moving the tuner for a total of 1 ½ turns in front of the muzzle in small increments finds a spot and chasing huge movements of maybe up to 20 turns is a long hard way to find a spot. Of course there could be a good spot in the middle. I use the bloop tube length to determine a starting point. The weight of the bloop tube determines the lift I desire. I then thin a bloop tube to reduce its weight to accommodate the weight of the thimble. In that way I can match a fundamental vibrations and sneak up on the other overtones and the launch angle. edit: because moving the weight follows the leverage principle and so I can effectively change the weight to a small degree which enables me to deal with trade-offs between nodes and compensation where the two best tunes overlap. This deals with minor variances of wave length and amplitude as best I can. We are interested in the harmony by way of the intersection of many orders of sine waves for the tightest group. I can see on paper up to about 4 vibration patterns, not just the fundamental wave, Varment Al found about 9 and Purdy may go to 19. Its the interactions of these waves and then the launch angle you have to optimise. But you must know which way to move for the two general forces then compromise on the overlap.

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.

[plumbs7]

Thanks David too! And yes I was blessed and still dealing with loss!

Ben , 34" is a lot for a 308 and in fact out local "The Rockstar" Josh is having great success with a 26" Saum with a damper ! So sometimes for once longer may not be better !

28-30" is better with the whole physics from my experience .

Regards Graham.

[scott/r]

Being a t/r shooter, would it viable to use my front tunnel to similar effects of a tuner by moving the mount forward or backwards?

[williada]

Yes Scott, when I was in State teams in the 1970.s many we doing just that but the knowledge did not leak. We used feeler gauges to keep a check on tuning distance but set and forgot them. Its been around for many years. I know of Qld's who did it back then too. Frank Pinion of SA makes a tuner to sit in front of your foresight. Just look at his centre counts. He won SA Queens last year. David Rich's tuner was a Pinion when he won US long range in TR. David.

[ecomeat]

Ben, I have already sent you a PM on the Denis Aarons FB page that you are a Member of, requesting your email so that i can send you a few attachments. Or PM your email address on here ?
Tony