Positive Compensation

[Curious]

I understand the concept with the exception of one specific point, can anyone help me out?

Is PC set up in such a way that it will only work fully at the specific distance it was tuned for?

If you tuned for say 800yds would you expect the load to show the same minimal vertical at 1000yds or equally 600yds or is it only at its best at 800yds?

 

[BoydAllen]

To have positive compensation you have to have the bullet exit the muzzle before the barrel has risen to its highest point during firing. This can be done by several means. Alex Wheeler would argue that a more flexible forend can contribute to the effect. Beyond that having a longer barrel (In Varmint Al's example he was starting with a typical short range benchrest configuration.) or adding weight to the muzzle of a relatively shorter barrel to slow its rise. He also calculated that turning down the barrel in its middle to make it more flexible could do the same thing, without the need for the weight or additional length. None of this would seem to be distance specific. That is not to say that tuning a tuner is the same thing, but you asked about positive compensation, which essentially is setting up a rifle so that bullets exit as the muzzle is rising rather than falling.

 

[R.Morehouse]

It will surely be best at the range it was tuned for. I am not sure if it will work almost as well 200yds either way. I would think it would partially depend on what your ES ends up being at your PC range. Low ES/SD i would think will take care of you at pretty much any distance once you plugged in the math for the come up.

Regards
Rick

 

[Keith Glasscock]

Do this: Calculate the ballistic trajectory of the slowest shot of your ES vs the fastest with the POI fixed for 1000 yards ( I can show you how to do this on JBM). You will see that the trajectory of the slowest shot will have to be substantially higher at 600 yards.

To answer your question: In real-world ES situations, the tune at intermediate ranges will be lesser compared to the PC tuned range.

 

[Alex Wheeler]

The whole idea is to find the tune where bullets of different speeds cross paths at the intended distance. That can only happen at one distance. But the tune will still shoot well at other ranges because its still in tune. My advice is tune at the farthest distance and the mid range will hold up ok. It doesnt always work the other way though. Keep in mind the PC tune is going to be very close to your normal load window. Its not like its in a totally different place. At short ranges the rifle will have a window. Where the barrel is slowing down, stops, and starts heading the other way. The rifle will group in that area and its commonly called the window. However the PC tune will be just one spot in that window before the barrel stops it upward travel. Which is why I keep saying theres no window at 1k.

 

[Curious]

If I had very low ES say in the 5fps range then will I ever really be seeing PC happening?

I understand the concept of different bullet release points on the upwards plane of the barrels movement. Ive also read about some guys who wouldn't bother with a chrono while tuning because in terms of PC it should be irrelevant?

Does that mean that the well PC tuned rifles typically show an ES of say 20fps or more or less?

 

[Alex Wheeler]

If I had very low ES say in the 5fps range then will I ever really be seeing PC happening?

I understand the concept of different bullet release points on the upwards plane of the barrels movement. Ive also read about some guys who wouldn't bother with a chrono while tuning because in terms of PC it should be irrelevant?

Does that mean that the well PC tuned rifles typically show an ES of say 20fps or more or less?

ES just is not a big part of this. You tune for PC and the ES is what it is. I have seen it in the low 20s and vertical is not effected.

 

[Stan Taylor]

ES just is not a big part of this. You tune for PC and the ES is what it is. I have seen it in the low 20s and vertical is not effected.

I had 29 es this weekend the rifle give me a 3.7 inch group at a 1000yd match I chronograph my record rounds trying out some different powder ev even though I think es is important but not that critical.PS if you notice in this picture I still have some vertical but that could be my gun handling that causes this I am not a slow shooter but not fast.

 

[Gilbert Garza]

I’m gonna ask the newbie question....what is positive compensation?

Can someone point me in the correct direction on this type of load development, please.

 

[Curious]

I’m gonna ask the newbie question....what is positive compensation?

Can someone point me in the correct direction on this type of load development, please.

Google is your friend Gilbert or try the search function here, there is lots of info

 

[alinwa]

I’m gonna ask the newbie question....what is positive compensation?

Can someone point me in the correct direction on this type of load development, please.

Positive compensation is this;

To start with, "a bullet is a fast rock"......... nothing more and nothing less.

So let's say you and a friend have a bunch of tincans lined up on a fence rail and you're throwing rocks at them. You find that you can hit more cans throwing HARD....... but then your arm gets tired so you "compensate." You lob the rocks higher but still manage to hit some cans.

Or maybe you're playing "Horse" on the basketball court and you shoot hard-soft-lob-loop-freethrow etc all DIFFERENT shots (trajectories) but all (hopefully) compensated to hit the basket.

This is the "compensation" part. This is what's "going on."


Now, bullets don't all leave the barrel at the same velocity. Nor can you yourself "compensate" for this. so the science of Positive Compensation involves getting your gun set up to self-compensate. Once you know WHAT needs to be done, now comes the HOW and for this you'll have to first of all procure an EXTREMELY accurate rifle, then you tip precipitously off the Black Diamond slope of the accuracy hill and go for it. You'll enter a frustrating and sometimes intimidating maze of opinions, facts and sometimes outright guesses and hopefully find the pleasure of a rifle putting one bullet on top of the other at given yardage.

Yes, a gun can only be set to ONE yardage........ in short-range BR the most common approach is to tune at 200 and expect a little vertical at 100. I have the luxury of a home range and the ability to shoot through multiple targets and can actually observe this action.

If I have one word of advice it is this...... don't even waste time thinking about compensation unless you've a system capable of shooting 5 shot groups under 1/4 moa. A 1/10 moa 6PPC will show results much more quickly.