.284W/180 VLD/AR2209/Lapua brass recommendations?

[williada]

I should have explained the micro pattern determination. Similar vibrations will cluster together and the odd shot out of the cluster is associated with a different vibration pattern. So some plots do not use a group centre method to indicate the sine wave. What I have attempted to do is isolate that different pattern which is the one that will screw you with this set of plots. That is the key factor in compensation tuning.

[DenisA]

Hi Dave, thank you very much for you analysis and explanation of my groups. There's a couple of things I'm not clear on though. I see that you've plotted the red line from the top of some groups to the bottom of others. I'm sorry if you've explained that in a past thread, I must have missed it. Also, do you feel that the low shot in the 51gn group is indicative of barrel trend? I put it down shooter error though I could be wrong.

Thanks again. I really appreciate your expertise.

[williada]

Hi Denis,

I have not explained this sub routine method of plotting in the posts so you did not miss it. I try to tweak up people's knowledge bit by bit as it is absolute information overload for many and I know I have had a lot to say at times which I am aware of. I gave Tony a full explanation of this method to flush out those frequencies which are part of the overall picture which are at the extremes of the group.

No, I don't think that low shot was you, as it sits on the trend line I drew as a line of best fit with those outliers. They are a good place to start when you have a double bottom (Stock trading Technical Analysis jargon) and track upwards following those outliers to find a peak by way of intersection coming from two different directions. As such it is not drawing a line of best fit through group centre. Its not the cluster which I am worried about, but the ones tossed to the extreme which I want to manage.

There is a lot more to this with further analysis when you take into the account each projectile speed and balance that with the extreme spread which can mean little about a node and the rotation of the groups like a spiral galaxy. It really should be called big bang theory and that's what I will call from now on. That's the part I would have to show people case by case, but due to time and energy I will limit it to a few who can pass on the knowledge at their local level.

Regards,

David.

[williada]

"If you eat All Bran you do not need All Bran" is what the ad. used to say. Just a little more on the extreme spread consideration. Hopefully readers could see that the extreme spread was not that significant if your projectile exited on a node.

Where it does matter is when you are between nodes and its impact depends on the proximity to the node and the direction the bullets are being tossed.

In terms of positive compensation, the bigger the extreme spread, the more distance specific it becomes for the tightest point of compensation. Technically we can induce a positive compensation for any distance if we pick the right point before a peak node or after a trough node.

With a neutral tune the low velocities can drop out at long range with more impact at six o'clock. If this range of neutrality has a broad channel, then expect the drops to be greater. You can pick up micro nodes of peak and trough with a neutral barrel. The position of the peaks and troughs in that channel whether they are higher about mid point or low in the channel also effect the amount of vertical displacement at long range. I prefer mid and above to cover for environmental conditions.

With a negative barrel, probably the best area you can find is a neutral section and look for a micro peak. The vertical displacements of this macro profile of compensation tend to get worse with distance.

You have to assess the widest window, even though there can be some real teasers. Usually either side of those teasers are poorer setups and if you have a teaser with a wide right outsider, look out. Beware of the groups that really hollow out like an antinode if the teasers are close by.

Remember, if a bullet goes out on an angle nothing is going to recover it, so in this sense if testing is done at a relatively short distance when coning forces have settled (about 130 - 140 yards) they are a good indicator of the long range pattern. The only thing that would change the course of a projectile is a mysterious wind strong enough to offset the launch angle. This can happen at extreme distance shooting through different wind zones. But its a remote possibility. So believe what you see on paper. The paper will tell you that if the groups are generally opening up despite being on a node or close by as you go to maximise velocity. I will go for group size every time and learn how to read conditions and match them with my expected group size. David.

[williada]

I split reading conditions into three broad areas which need to be mastered by coaches.

Firstly, the wind allowance for strength and direction, the wind zones and counter zones and the effects of terrain and micro climates.

Secondly, the Magnus force effects on elevation, particularly for long range where left wind lowers and right wind raises the projectiles with drop offs having the opposite effects and sometimes a drop to 6 o'clock when there is insufficient lift force. It is important for team shooters to have the same calibre otherwise its a nightmare for coaches to learn and judge.

Thirdly, that has to be evaluated, are the effects of mirage on the apparent aiming mark shift and this has to be viewed as three different densities and therefore three sets of allowances.

Reading conditions is exacerbated, if the scope and bore line are different because the zero will be different as distance changes. This means the spin drift which relates to Magnus force seems different and it also applies a different perceived measurement of Coriolis effects at different venues. The only remedy for this is a muzzle aligned in the vertical. This has a profound effect on big bang theory, but sometimes one has to allow for barrel torque so that the bullet exits in the vertical plane. This can be determined from angular displacements in the short range testing.

Edit: For those that nip up their barrel's chamber every 800 rounds or so make sure the same vertical alignment is maintained, and in doing this, allow for a complete turn in the barrel for the length of the chamber nip up.

David

[DenisA]

Hi Dave, thanks again for your help.

To be honest, when I shot the 6:00 flyer in the 51gn group I really did feel like my technique was consistent with the other shots. Seeing as the it was in a long node, I started doubting myself and looking for a reason I guess.
Having read your input, I'll trust my technique, go with your advice and test the neutral section of 50.1gn through to 50.5 gn in .1gn increments.

I'll be sure to repost the results and hopefully chronograph the shots and the list their individual POI.

As always your knowledge is inspiring and REALLY appreciated.