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

[DenisA]

Hi guys,

I know it needs to be tested, but just to get a general idea.

I'm just trying to understand where a compensated long range load might be powder charge wise in respect to a great water line short range load.

Using my 6BR as an example at 100 yards, I have a very tight node from 30.4 - 30.6. 30.5 is senstaional. 30.3 and 30.7 are very similar in pattern and starting to open up to .5moa.
At 300, 500 and 600, the vertical is still waterline . 800, 900 and 1000 started seeing some vertical shots . (off topic, it's difficult to say for certain that compensation tune is the cause as it was very windy and the mounds at Belmont are notorious for this, especially since the 700's been built up,,,, in my opinion).

If I had the opportunity to test loads at 1000 yards, would I find that the "BEST" compensated tune would most likely be within .02gn either side of that great 30.5gn short range load or would it most likely be a completely different load/node?

Cheers.

[AlanF]

Denis,

Its very uncommon to find a barrel/load combination that will fully compensate for velocity variation at 1000 yds. What you will generally do is find something that fully compensates at some closer range, and that is the best you can do. Any further improvement needs to come from reducing your velocity variation. The best way of finding a load which gives maximum compensation is to use a ladder test (at say 500yd), and look for a downward slope on the graph (assuming your plot has the POI height plotted on the y axis). It will require an extremely steep downward slope to compensate fully at 1000yd - I have never seen anything close.

Alan

[DenisA]

Denis,

Its very uncommon to find a barrel/load combination that will fully compensate for velocity variation at 1000 yds. What you will generally do is find something that fully compensates at some closer range, and that is the best you can do. Any further improvement needs to come from reducing your velocity variation. The best way of finding a load which gives maximum compensation is to use a ladder test (at say 500yd), and look for a downward slope on the graph (assuming your plot has the POI height plotted on the y axis). It will require an extremely steep downward slope to compensate fully at 1000yd - I have never seen anything close.

Alan

Thanks Alan. That's confused me a little more. I thought the whole point of compensation tuning was to develop a load thats tighter at the longs than short and mid range.

Are you suggesting that's also the case with low SD loads and heavy bullets that retain a higher % of MV at 1000 yards.

[AlanF]

Denis,

Compensation describes a situation which can happen at any distance, where the vibration of the muzzle is on the downward part of its cycle. In this situation a slight decrease in velocity causes the muzzle to point higher, and an increase in velocity causes the muzzle to point lower. This is the opposite of what happens ballistically, where a faster bullet does not drop as fast as a slower one. Full compensation is achieved when the two effects cancel out i.e. a faster bullet points lower out of the muzzle, but doesn't drop as fast, so hits the target at the same elevation as slower bullets. If you understand that, then you will also see what I meant about in the previous post.

Alan

[pjifl]

Obviously, different cartridges, bullets and distances require different compensation.

Let's take an extreme example just as an illustration.

If you have a rifle/barrel that shoots 2 minutes high when the velocity is 40 ft/sec low at 50 yards, then it will be compensated nicely at 1200 yards.

It is easy to load so Velocity deviation from the mean is less than 40 ft/sec. But many people have a variation from lowest to highest velocity of this - especially over a 20 shot shoot.

Really careful loading will reduce this much much further and is a proven approach.

I know of no serious target rifle used today that would be whippy and springy enough to achieve this because one of the contributors towards extreme accuracy has been to eliminate vibrations as much as possible.

If you seriously wanted to investigate this further, you could deliberately induce massive barrel vibrations by using an offset weight near the muzzle.

Unfortunately, even if this weight is offset vertically, it will also increase lateral vibrations as well. The vibration is a 3 dimensional phenomenon.

It may be that at 900 or 1000 yards there is a best compromise that is worthwhile. But the setup would be hopeless at short range unless one used perfect ammo.

Peter Smith.

[DenisA]

I do understand that Alan. I'm not sure now of where the advantage would be in compensation tuning the 6BR for example.

With the current 100 yard developed load, it shoots competetive vertical out to 800 (because 800 has the largest scoring rings).

The way I imagined the rsults to be, if compensation tuning meant that I could find a load with x ring vertical at 1000 yards, then it seemed worthwhile to have 2 loads. A short range and a long range.

Are you saying that compensation tuning may only buy you another 100 yards or so over a load developed at the shorts?

Assuming that all examples are low SD loads and the same barrel profile, is a heavier bullet that retains more energy and % of MV at 1000 yards more likely to be able to be compensated at 1000 yards than a small bullet who's MV, BC deteriorates more rapidly? or are these advantages of the bigger bullet cancelled out by a heavier vertical barrel vibrations and higher amplitude of muzzle angle?.........................assuming that a heavier bullet/cartridge has a higher amplitude of vibration.

Thanks for trying Alan, I'm not the sharpest "tool" in the shed.

[DaveMc]

As Alan, Peter and I have stated before; compensation tuning has very little effect at 1000 yards with modern target rifles. Your heavy barrel, traditional bedded rifle is unlikely to give you enough compensation to achieve what you are looking for.

The elevation issues you are seeing are more likely due to two things. Velocity variation and BC variation. - It is possible that you have compounding negative compensation but it is unlikely to be a major issue and you will have to move the velocity range you are currently using by around 70-100 fps (or more) to see the reverse.

Many, many barrels / rifles / loads act as yours does and can be accurate at short range but fall apart at the longs (VERY TYPICALLY DEMARCATED BY 700m/800 yard target, getting bad by 900 and unacceptable by 1000)


If you want to see the potential for compensation with your setup then shoot a long ladder (say from 27 to 31 grains) at short range (25-500 yards) through a chronograph and plot elevation against velocity for us (also elevation against load). Post the results and we will discuss. It is best to do the short range test first to eliminate (or reduce effect of) BC variations and where you know your rifle is accurate. With some simple calculations you can roughly determine how much compensation you will be getting at various ranges (angular velocity imparted on projectile by barrel vibration is constant - so is linear with range).

I expect you will see some significant periods where the elevation trend actually drops with increasing velocity at short range. somewhere around 3-500 yards it will be flat and then after that increasing velocity will cause an increasing trend in position on the target face. At 1000 yards you will hardly notice a blip in the graph.

[DaveMc]

ps Another point that seems to be often misunderstood.

We are actually trying to impart (or find) an upward movement on the muzzle as the projectile exits. To think about this logically, a faster bullet will arrive earlier and needs to be leaving at a lower point. A slower projectile needs to exit at a higher point.

[DenisA]

ps Another point that seems to be often misunderstood.

We are actually trying to impart (or find) an upward movement on the muzzle as the projectile exits. To think about this logically, a faster bullet will arrive earlier and needs to be leaving at a lower point. A slower projectile needs to exit at a higher point.

Ahh, of course. If it were on the downwards movement the faster bullet would exit higher and the slower, lower.

Seems simple enough, but saying it helped.

My node is after an incline in test group impact height and therefor if I were to go looking for a specific mid range compensated load, I should be testing under my 30.5gn. (Not that I could go looking much beyond 30.5gn in a 6BR anyway).

That helped with my original post Dave. Thank you.

[AlanF]

ps Another point that seems to be often misunderstood.

We are actually trying to impart (or find) an upward movement on the muzzle as the projectile exits. To think about this logically, a faster bullet will arrive earlier and needs to be leaving at a lower point. A slower projectile needs to exit at a higher point.

Dave,

Now I'm a bit confused . Are you saying its about the speed and direction of muzzle movement as the bullet exits rather than where the muzzle is pointing as the bullet exits (maybe its both)? I guess for the purposes of ladder testing it doesn't matter exactly what happens at the muzzle, but interesting to think about.

Alan

[pjifl]

Just a thought.

I cannot remember if you have mentioned actually measuring velocity spread or not.

But, unless you do this, there is no way to really know whether you are really getting compensation or not, or whether you are simply reducing the angular dispersion when you make loading changes.

To investigate compensation you really need to deliberately introduce a known velocity variation then relate this to impact points at different ranges.

Just because the rifle shoots well does not prove there is compensation. It could simply be that you have a perfect loading technique.

Peter Smith.

[DaveMc]

A hard concept to grasp Alan but either way - if the barrel is moving up or angled up both versions impart a vertical velocity component to the projectile. For a different vertical component we actually need to change the angular velocity and this comes mainly from the barrel pointing in a different elevation.

yes I meant the barrel muzzle is moving up (changing angle) but only in reference to where it is pointing at the time of exit.

Dave

[pjifl]

I once saw an attempt to mathematically analyse the relative effects of the vertical velocity flip and angular direction of the tip of a barrel on launching a projectile.

The conclusion was that the angle had far far more effect than any flip from the muzzle.

I do not known if experiments and high sped photographs have born this out but it sounds reasonable to me.

Not sure if this is very important to us, however.

Peter Smith.

[aaronraad]

...and here I was thinking that you simply slid/screwed on a barrel compensator and then went out and cranked the load development right up, tweaked your seating depth etc. so your load produced the highest muzzle velocity with minimal ES; then using that same load you simply moved the barrel compensator back and forth until you got the group size and shape you wanted.

[BATattack]

So if first and foremost we need to lower our ES as much as possible? What things do you feel have the biggest effect on ES and in what order do you feel they should be prioritized in?

Once velocity is reduced to its minimum practically possible would it be best to artificially induce ES by loading several batches of 10 rounds .2gr above and .2gr below your desired charge weight then testing tuner settings?