Compensation Tuning Again?.......... Sorry!

[williada]

Aaron I will have to find an old data disk, but from memory .3075 x .299 in 1-13 was the best performer for that Winchester Palma case with old Sierra 155.

[DenisA]

Wow Dave and Dave, theres a lot of info that I'll need to read a few times to let in sink in......... if it does.

Regarding my 6BR having vertical shots at 800 and out, I'm now pretty convinced that it's not to do with barrel compensation or lack there of. Yesterday my shoot at 1K had much less than .5moa in vert. Maybe .3 moa. The waterline was sensational in an extremely light condition that was only 1 moa of left wind with no head, tail wind and only very gradual velocity increase to 1.5 moa over the detail. In my mind that proves beyond doubt that the large mounds from 700 yard onwards, combined with head and tail winds are responsible for the vert that I had previously experienced at Belmont. Maybe other factors also at play such as light variation and/or hot air pockets, but I'm confident its not a compensation thing.

I was watching another great shooter who uses a straight profile 1.25" barrel in a alloy chassis and noticed a lot of barrel vibration after each shot. The person I'm talking about always shoots great scores with high X counts.
It made me wonder if you could have the best of both worlds by using a heavy barrel in a rigid stock for the short and medium ranges and instead of a flimsy barrel for the longs for extreme compensation, use a stock with a flimsier forend at the longs to increase the amount of possible compensation. If thats the case, maybe a stock with a tension adjustment on the forend would work.

Just to clarify, I no longer think that barrel compensation is currently relevant to what I'm trying to achieve, but the theory's interesting and I do want to understand it and its characteristics.

Thanks for all the info Dave'n Dave..

[johnk]

I would really like to see someone deliberately investigate both the compensation possible and the accuracy potential from a relatively light barrel using offset muzzle weights.

Peter,

In 2006, Laurie Ingram showed me a tuner he had worked with, essentially a standard peep foresight with the tunnel threaded for a rod jammed by a nut. Not unusually, he was heavy on prognostication & light on data.

John

[williada]

So Denis, it sounds like you need something with more mass to smash through those aberrations like a 7mm or 30 cal.?
I have seen that condition in the tailwind at Bendigo. I might just have to rethink my 6mm Long Dasher Ackley now. I have a spare 1-10 in .30 hmm.

[RDavies]

So Denis, it sounds like you need something with more mass to smash through those aberrations like a 7mm or 30 cal.?
I have seen that condition in the tailwind at Bendigo. I might just have to rethink my 6mm Long Dasher Ackley now. I have a spare 1-10 in .30 hmm.

Dennis, you beat around 35 or so 7mm shooters at 1000yds with your puny 6BR to get a 60/60 at 1000yds at Belmont. I'm not gonna try to help you.

[DenisA]

Dave, my .284 came to its competetively accurate demise some months ago and I hadn't picked up on it being the issue with my shoots until too late and too close to the Queens. I hadn't left myself with enough time to break in and develop the second barrel. Won't make that mistake again.

I have a 300wsm which was intended to be my 8, 9 and 10 gun. I shoot great groups off the bench and haven't had the same success prone. I've recently identifed through videoing both situations that technique is the issue and I need to work on that a lot before I can make it competetive prone.
Off the bench, a seated body recoils with the rifle beautifully with only the slightest forend torque. Shooting prone, an anchored shoulder as a stop causes the forend to jump aggressively. Although the recoil doesn't hurt and flinch is not an issue, stepping up to that extra recoil level from something like a .284 requires A LOT more technique control. I feel it almost needs a compromise of full travel free recoil but with full cheek weld, which is a contradiction and not natural in the prone position. I'm sure an accurate compromise is achievable as a shooting friend of mine seems to have it tracking and shooting well prone.
I believe the 300wsm will be a force to be reckoned with if I can find the correct prone technique.

All that said, having no option but to shoot the entire QRA Queens with the 6BR really re-opened my eyes to it's potential. I started F-class with a 6BR and when I began playing with larger calibres I lost the understanding and trust of the 6BR's ability.
Last week has made me re-discover again its inherent accuracy out to 1K. In consistent conditions of any reasonable velocity it can deliver high X counts. When the conditions are varying through any velocity the 6BR will easily drop points and requires a much higher level of wind reading, response and strategy.
I found myself thinking that hyperthetically trying to master a 6BR in all conditions could still be extremely competetive against the likes of .284's.

DaveMc gave me some good advice that I will follow. Although it's SENSATIONAL to shoot with, I'll use the 6BR only for club events and to hone my wind reading skills and I will be sticking to one larger calibre for competition.

[DenisA]

So Denis, it sounds like you need something with more mass to smash through those aberrations like a 7mm or 30 cal.?
I have seen that condition in the tailwind at Bendigo. I might just have to rethink my 6mm Long Dasher Ackley now. I have a spare 1-10 in .30 hmm.

Dennis, you beat around 35 or so 7mm shooters at 1000yds with your puny 6BR to get a 60/60 at 1000yds at Belmont. I'm not gonna try to help you.

Bahahahaha, your too generous Rod. The only reason for that success was the same reason some on here are lobbying for squadding.

I also shot some of my most embarrassing scores at some of the shorter ranges.

[williada]

Too deep.

[DannyS]

Thanks David, fantastic reading.

Cheers
Danny

[DenisA]

Too deep.

Sorry Dave, I'm not following?

[DannyS]

Hi Dennis, David posted a very in depth comment, which was great reading. So I made my post and by that time he had deleted his.

Cheers
Danny

[DenisA]

Hahahaha, thought I'd missed something. Thanks Danny. I was pretty sure I've never had a deep thought in my life.

[mike H]

Too deep.

Sorry Dave, I'm not following?

Fortunately I read Willada's information before it was deleted,for me it was not too deep,and I can be challenged with scientific /mathematic data fairly easily.
Lot's of good information there.Made me think of all the knowledge that get's lost and then has to be rediscovered . I respect the decision to delete the material,I hope he will pass more of his store of information and history on.
Mike.

[williada]

Well Denis, I pulled it, and I thought early enough but some of you buggers get out of bed before me. I thought the writing was snowballing and I didn’t want to be a keyboard cowboy, I would rather be shooting.

So in order to cure some, I have added to it and hand over the baton to others. Sorry Denis for the confusion. The original draft was one hit, but the general tenor is accurate.




For Danny S who likes to read and Aaron who wants to know more, I can’t locate the summary data disk as yet and it’s about somewhere since I produced it and presented the information to the NRAA councillors and the Australian PalmaTeam on different occasions. It has survived packups from 3 bushfires in the last 10 years. So you and others may be interested in this stuff in the meantime.

Musings on experiments to the best of my memory then, with some background.

The grooves and bores of .30 calibre have changed size considerably with the history rooted in the International Bisley competitions in England. I believe it was Boots Obermeyer, an American who realised the groove .3065” was the way to go with the English matches simply because the bullets were undersized with the advent of 7.62mm Nato rounds used in competition compared their .30 cals (30-06). So barrels in this size were used due to their success in 1-12 with a 2 degree leed angle and have continued to be used by a few albeit with different leed angles. It was thought by some, these tight barrels ironed out the lead core like a rolled smoke and produced a better gas seal with the projectiles whose jackets where harder than the ones used today. Consequently land depth was sometimes a thou deeper than we currently use to ensure the bullets engraved with a better gas seal which leads to lower extreme spreads but didn’t matter a tinkers cuss in machine gun fire which they were designed to cope with too. Those swaged projectiles even grew longer and if you think about it would technically increase BC ever so marginally. In more modern times, .3065” groove/.298” bore and .3065/.299 have been used successfully, but the Pressure Trials Consortium 1998 Chaired by Dr. Geoffrey Kolbe of Border Barrels fame, led to the mandating of the Bisley chamber with a throat of .3085” for safety after their experiments with barrels of different internal dimensions. However, I think there is a sleeper in matching internal dimensions and engraving forces for the right bullet bore interference fit given the generally accepted parameters which trials at Aberdeen USA have worked through as I understand it as well. I think the long range accuracy of tight barrels was also influenced due the minor lift of the muzzle induced by the pressure on the 2 degree leed, and hence that small compensating ability if tuned with the right barrel profile. So many assumptions and interrelationships have to be tested as certeris parabus models i.e. assuming other variables are constant while examining the one of interest. Border has got this down to a fine art now, in my opinion, with their computer modelling. Nowadays ballisticians can use very sophisticated ballistic programs as I was fortunate to be privy to relevant research so long ago through a third party in the Defence Department assisting project Penumbra with regards twist rates and materials simulation used in construction of projectiles, particularly jackets (probably “Prodas” software) in a sophisticated way like engineers use the program “Solid Works” with materials; and work by a son who examined mono metal solid bullet construction and barrel catastrophic failure in his 4th year honours Engineering projects .

The next major development after Obermeyer, probably came from George Swenson one of the co-inventors of the Swing Action, who I believe worked with Shultz and Larson. The Shultz barrels cleaned up with 1-14 twist and .3074 groove for the 144 grn. with I think, a 1 1/2 leed angle. The Shultz barrels in Australia soon overtook some tight .3065 groove of Black Mountain Barrels which were hammer forged as opposed to cut and buttoned barrels. The barrels Omark produced, and later MAB soon began to look similar to the Shultz and Larson profiles except shorter and marketing had several makers listing 1-12, 1-13, and 1-14 twist rates with common leeds angles of 1 1/2 degrees for the 144 grn 7.62 mm NATO round. Then Shultz and Larson changed hands and the barrel profiles started to change and emerge as a shorter faster taper and eventually lost market share here. Some Shultz’s made for Omark actions were considered soft and throats wore quickly and I still have one to remind me how bent a barrel can be. Their early gear was fantastic. It wasn’t until Border Barrels come on the scene that we saw barrel profiles change again and we saw 1 ¼ leed angles being used with projectiles similar in shape and drag as the Sierra 155 with soft jackets compared to the old 144 grn. Perhaps they were looking for less lift on the other side of the equation. And we have since seen the projectile range grow for shooters in TR and F/TR to Dyers, Sceners, new Sierras, Hornady, Bergers etc. The Border barrel I owned tended to be larger with .308 groove/.300 bore and similarly Madden barrels were larger. They were fast barrels. I think they both ran 4 groove barrels with a standard land height of about .004”. From memory True flights were about .3075 in the groove. Barrel makers tend to use a bore groove volume ratio to give the same displacement value suitable for engraving, maintaining bullet integrity and safe pressure with more or less lands and grooves they decide to use. CIP and SAAMI have set the standards for chambering and such of the like. If you think about a microgroove barrel, they have many lands but they are shallow. The Tobler barrels I used at one time were 5 grooved. The theory being that this impacted less on the jacket and balanced the core. My thinking was the boundary layer in flight around the projectile didn’t care too much about the extra groove and if you think back in time, 2 groove barrels were used successfully albeit on large targets for the times. As an aside I think land height has to be sufficient in height that the projectile does not strip. I have still got several test barrels from the 1980’s that are unused with four grooves but with a land height about .002” in .308. I was looking at reducing friction. A similar barrel won a regional championship for me. The down side was wear. We are now seeing canted lands appear, but I believe it was Boots Obermeyer who could claim the early development of them. Interestingly, I was told Krieger once worked for Boots and I think someone in Border learnt their trade from Boots too.

I also remember people quoting Warren Page’s book circa 1973-6, and some of the thinking is still used by many of our shooters today as the book was sold through the VRA. He stated in, “The Accurate Rifle, “...we cannot see any difference in accuracy if the barrel is held within .003 inch the same size either way of the bullet.” I disagree. I don’t think this acceptable as per Pressure Trial Consortium or my testing at long range. There appears to be an order of magnitude discrepancy with the bullet barrel relationship in the print. I found with the old Sierra 155 ran best with a .0005” reduction on the nominal .308” diameter and more like .0004” because the reamers cut oversize. For a rule a thumb, with all due safety considerations, experimenters in other calibre sizes could use the same ratio in testing this relationship. It is work I have not done. I have not worked with canted lands and you would have to consider jacket hardness and engraving forces.

So where are we going with this, and it only dawned on me when I tested pairs of Kriegers in .3065, .3070, .3075 and .3080 and played with throat angles from 1/2 degree, ¾, 1, 1 ¼, and 1 ½ degrees that I noted barrel lift barrel lift varied correspondingly. I reckon Boots knew that and passed on this knowledge hence the early 2 degree leed to lift the muzzle. So I played with my Border barrel and True Flights and realised the connection to profile and leed angle. You can physically feel the hit on the shoulder from a steep leed and hardly notice it with a shallow leed and it is indeed a general balance between profile and leed angle for accuracy in .308" calibre. The shallow leed and 1-15 barrels I tested were a dream to shoot at short range for comfort, like shooting a free recoil technique. Accuracy is certainly induced from better bag handling like a 6mm br. Twist rates of new barrels tested included barrels of my own, those from the NRAA, and a couple from the team armourer were 1-12, 1-13, 1-14 and 1-15. The muzzle velocity the old Sierra loved at Rosedale over 1000 with reloads was 2970 fps and it took a 31 inch barrel to keep it over 2950 fps with factory ammo to keep it past the transonic range at 1000 yards. I also believed the drag on the bullet was fairly minimised for the local conditions at this muzzle velocity (2970 fps) and nothing was to be substantively gained from driving them harder. The drag was probably reflected in the smoother oscillations of the sine wave under the test conditions.

Also now reflecting more on the small regular velocity oscillations in an earlier post (as picked up by the chronograph) when it did not always correspond to barrel heat and pressure as graphed; the reasons could be a sign of physical internal yaw induced by a lack of concentricity or throat diameter causing bullet slap and vibration, but to exist down range after coning effects (transitional yaw) to emerge as angle of yaw, then to slow oscillations called precessions, as the magnus moment tries to rotate the bullet perpendicular to the longitudinal axis of the bullet but is damped by the gyroscopic (centrifugal) effect of the rifling can be explained. Now as I understand it, if the centre of pressure of the Magnus force (an aerodynamic force) is behind the centre of gravity, the projectile will be stable; and if on the other hand it is in front of the centre of gravity the yaw will increase hence the oscillation of the sine wave because the gyroscopic force is greater. This means that the stable nature of the oscillation has to be velocity specific for a given air density. So as the bullet is slowed down, the small precession grows and at the end of its trajectory the bullet becomes unstable. Perhaps this could be reduced by better bullet design, but maybe we have not found an ideal velocity for the range we are shooting. It has implications for the bearing length of the projectile as well as the ogive. It sure has implications for overzealous shooters trimming their metplat back too far. Therefore I feel there is a strong case for short, mid and long range rifles for extreme accuracy the supercentre now demands and an across the course rifle will not cut the mustard against those with more resources in the future.

But generally speaking now, every barrel is different in its refinement for accuracy. The tests from the machine rest were relative to each other. Other factors such as internal concentricity of bore with external profile varies in most barrels and that’s what makes every barrel different in my opinion as well as how barrel curvature is set up in the vertical plane, besides hardness and materials and their production variance, right back to the crucible and where in the mix it is tapped from to form the stainless steel used. Let alone the fork lift driver who picks up the billets at every stage of shipping and handling, and bends the long billets. I saw this and worked on blanks that were bent in the 1980’s. Let alone the certification of steel state, depending where it is sourced from, often actually varied from independent hardness testing or the second stage of heat treatment that could be skipped by accident as has happened in Australia with heat treatment in the case I think of a buttoned barrel in its manufacture that contributed to catastrophic failure. No names, no pack drill. So the moral is to source steel from reputable producers and follow quality procedure. For what it’s worth, I prefer cut barrels for less stress as they don’t open up like buttoned barrels can when they are re-profiled. I can say all the tested Krieger barrels tested and groups with the old Sierra were close to one minute and most less at 1000 yards for ten shot strings in elevation with 1 ½ degree leed and .010” jump from the machine rest with the factory ammunition. This was verified by Peter P (edited for privacy) who was present at these tests and Vice Captain of the Australian Team at that time.

Cutting back to the chase, the implications for leed angles are twofold. If you want barrel lift go with a steep leed. This effect is reduced by shorter stiffer barrels. A half degree throat will be well suited to free recoil where barrel lift is moderate. I will leave it to you guys to think about jamming a projectile into the lands in terms of lift, rather than concentricity or efficient powder burn. There is more than one way to skin a cat for accuracy. Of course Lilja has a site where he explains the leed angle in terms of tangential match with the ogive. I’m sure that loading into the lands and throat wear mitigate against this set-up to some extent and everything is a trade off. Of course projectiles wear their own shape over time. The only caveat I place on it is, that these characteristics work while the throat is relatively fresh, so that 800 round re-chamber is significant for those with the resources. Otherwise that purple patch we see will disappear until we wear the throat out to the next node as seen on the target. Too often shooters blame themselves for a form slump when they should be chasing up the free flight as well. Do this sooner than later because the bore scope will reveal the 6 o’clock wear in the throat due to bullet slap in most rifles and it is often highlighted by that shiny new chamber when the barrel re-enforce has not been cut back far enough in accommodating the new barrel tenon.

While it is counter intuitive, the tighter barrel, the slower it was and I deduced the higher pressures were swallowed up swaging the projectile down because the projectile does not miraculously grow once it has been grabbed by the throat with higher peak pressures, closer to the breech as indicated on the Pressure Trace in later tests on other barrels.

I also believe that flat based bullets are better at gas sealing and produce low ES and that’s why we see them consistently perform better up to two hundred yards and after that the drag factor in the boat tail bullet generally takes over. I will say that loose chambers, a non concentric chamber or a misaligned bolt face perhaps due to wear on the 6 o’clock locking lug has a greater chance of gas slapping the boat tail bullet out of alignment with the bore. I think throat diameter is more important than length and should be tighter than looser for alignment purposes. Remember the reamer will cut bigger than the size indicated on it unless it measures less.

I cannot comment on VLD projectiles as I have not tested them, but I will say the Dyer with a bigger bearing surface shot better in the larger bore sizes. They had a nice BC in terms of external ballistics. Maybe this is relevant to VLD projectiles. As a further comment in relation to the theory on aerodynamic investigation and centre of gravity, the length of the bearing surface and ogive shape need more consideration in terms of the velocity range for tight grouping . Perhaps there lies the anomally why sometimes bullets with a lower BC can outperform those with high BC set in the wrong velocity spread. We tend to think people are capable wind readers. I always make grouping ability the highest priority. I might be wrong.

Before I close, people are often worried by the air gap in their case above their powder. It doesn’t matter so much with faster burning powders. The marriage between slow burning powders, primers and powder column ignition changes more when air density changes. If atmospheric conditions alter we tend to be pushed off the accuracy node. It becomes a timing of bullet exit with the sine wave peak. Now consider in terms of bore time whether more oxygen through air gap volume could assist or detract from that efficient burn? It is common practice for racing car drivers to adjust their air fuel mixture depending on air density. Just a thought. Some colonels load to the last kernel without breathing.

It is now for others to take experiment further if they wish to do so, discount or build on the information. I don’t think there is more I can pass on in the posts that I have not already done. But above all, have fun. It’s not about sheep stations. David.

[pjifl]

I read your original post very late last night. Tired, tired after returning - driving 100 Km - after shooting.

And I was also disappointing when you pulled it because I was intending to reread it this morning.

So - I am very glad you have put it back up and edited it a bit.
It actually answered a few questions I had about the historical development and reasons for certain specs.

I am not sure where this information should go - I feel it is a bit out of place here.

Maybe we need somewhere for historical technical stuff like this.

Peter Smith.