Range Report Let's talk about dispersion...

[BryanLitz]

Lately I've become (re)interested in the peculiar behavior of some rifles to shoot <span style="font-style: italic">angularly</span> smaller groups at longer ranges. For example, a rifle that shoots 1" groups at 100 yards, and 1" or 1.5" groups at 200 yards.

There have been many long winded discussions about this weird behavior but none that have definitively locked it down (to my satisfaction anyway). One of my theories for how this can happen is incorrectly adjusted parallax, ie, aiming error. My 6-dof modeling doesn't reveal any flight mechanics that could produce the non-linear dispersion which is why I settled on an optical theory.

In the spirit of information gathering and problem solving that the internet makes so convenient, I'd like to ask anyone who's seen this behavior <span style="font-style: italic">systematically</span> occurring with their system to post with the following information:

Rifle, barrel, twist rate, bullet, scope, and the ranges that the non-constant dispersion was observed. An example would be:

Rem700 in .270 Winchester, factory barrel, 1:10" twist, Sierra 150 grain GameKings, Tasco 3-9 w/ no parallax adjustment. 1" groups at 100, 1.2" groups at 200.

If your scope does have adjustable parallax, please be honest about how careful you are to set it properly for each range you shoot. Note that turning the dial to the range you're shooting doesn't mean the parallax is adjusted correctly. Most of those range scales on scopes are not right and the side-focus ones are the worst. You have to turn the parallax adjustment while moving your eye across the eyepiece and seeing if there's apparent movement in the reticle. I have a scope that needs to be set at 250 yards to have the parallax be truly eliminated at 100 yards.

Thanks guys,
-Bryan

 

[AQC440]

Re: Let's talk about dispersion...

Ruger 77 in 22-250,factory barrel, 1-14 twist, Sierra 52 grain match. 1" @ 100, 1-1.3 @ 300
This was not a fluke just happening one time. The rifle produced these results 10's of times.


Leupold fixed 12X AO

 

[Grump]

Re: Let's talk about dispersion...

No, I don't have anything that does that, but I want to give Props to Bryan (even though his Mommie has him spelling it WRONG) for finally starting to look at this reported phenomenon from a scientifically rigorous perspective.

At least, that's where I am expecting this to go.

The missing element is a report of the optic used on the rig...

...

...

...

Followed by testing of the optic's true parallax setting if fixed. And brutally honest reporting of how diligently the shooter adjusts the parallax for those with AO or SF capability.

I have high hopes for this going where "Mythbusters" so often only pretends to go.

FYI, I was totally spoiled by reading my Daddy's back issues of The American Rifleman, from the days when many articles were written by machinists and others who understood elimination of variables and sound testing methodologies.

 

[jrob300]

Re: Let's talk about dispersion...

Grump,

I so realate to what you're saying...


I used to think this was a long/heavy bullet phenomenon, until I started getting better optics and learned how to check/adjust for parallax. Then, voila! A lot of it mysteriously disappeared!

Most of my shooting is fairly linear now with regard to angular displacement of the shot. Out to a couple thousand yards. (the longer the distance, the fewer the data points.)

John

 

[bohem]

Re: Let's talk about dispersion...

I've seen it happen with 1 rifle in particular but I have never been particularly keen on checking the parallax. I'll see if I can reproduce the results and set an experiment out on it for you to log some data.

If it does end up being parallax I think I can help with that as well, I have a second rifle that has thus far not shown a tendency to do this but maybe fiddling with the parallax will make it show up.

It will probably take me a few weeks but I'll see what I can do for you.

 

[WRM]

Re: Let's talk about dispersion...

Hi Bryan,

I was so glad to see how it was addressed in your book - I concurred wholeheartedly with your conclusions, and wondered if you had read some of my previous internet discussions?... We had a real knock-down, drag-out discussion on Accurate Reloading forum several years ago....

Personally, I believe this is basically impossible. For example, there is no way that the bullet that hits low at 100 is going to know to "move up" with the rest of the group at 300 (and vice-versa).... And for those folks who think that VLDs have to "go to sleep", there's a photo in a recent Precision Shooter mag of <.1" group at 100 w/Berger 6mm VLDs, so that would blow that theory out of the water? I'll concede "go to sleep" as far as yaw angle settling down, but that is bullet yaw, and NOT "displacement" (trajectory/bullet flight path).

Being from the Show-Me state, I don't want to hear "that's what my rifle does", I want indisputable proof. I have an experiment planned to shoot two distances simultaneously, but haven't had a chance to conduct the experiment, yet. I have a friend who swears his 260 does this (SP260), and one of these days we will do this.

I plan to put two targets at 300 (one for him and one for me), put 300 dope on rifles and center on targets. Then without disturbing the rifles, dial 100 dope and put a second, single sheet of paper at 100 (desk blotter paper), and put aiming pionts on the crosshairs at 100. Then we both shoot groups, and compare the groups sizes.

I have 100% confidence that the 300 yard group will have equal or greater moa dispersion as compared to the 100 yard target....

I'll make sure you get the results!

Anxiously awaiting your conclusion,

Bill

 

[TiroFijo]

Re: Let's talk about dispersion...

I have never seen this "shrinking group (in angular terms)" happen, at least repeatedly and in a way I can be confident that is no fluke or due to shooer/parallax issues.

 

[jrob300]

Re: Let's talk about dispersion...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WRM</div><div class="ubbcode-body">And for those folks who think that VLDs have to "go to sleep", there's a photo in a recent Precision Shooter mag of <.1" group at 100 w/Berger 6mm VLDs, so that would blow that theory out of the water? I'll concede "go to sleep" as far as yaw angle settling down, but that is bullet yaw, and NOT "displacement" (trajectory/bullet flight path).</div></div>

Not to go too far down this rabbit hole...

But like I said, I used to be in this camp... now not so sure.

IF there is a bullet yaw problem, would it not show up as out of round on paper at some target distance? Perhaps the numbers we're talking about are too small to measure that way, but I would think that yaw issues would be somewhat simple to detect. And like you said, How does a yaw problem influence a flight path that goes out of line and then converges at some further distance?

John

 

[WRM]

Re: Let's talk about dispersion...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jrob300</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WRM</div><div class="ubbcode-body">And for those folks who think that VLDs have to "go to sleep", there's a photo in a recent Precision Shooter mag of <.1" group at 100 w/Berger 6mm VLDs, so that would blow that theory out of the water? I'll concede "go to sleep" as far as yaw angle settling down, but that is bullet yaw, and NOT "displacement" (trajectory/bullet flight path).</div></div>

Not to go too far down this rabbit hole...

But like I said, I used to be in this camp... now not so sure.

IF there is a bullet yaw problem, would it not show up as out of round on paper at some target distance? Perhaps the numbers we're talking about are too small to measure that way, but I would think that yaw issues would be somewhat simple to detect. And like you said, How does a yaw problem influence a flight path that goes out of line and then converges at some further distance?

John </div></div>

Agreed. Once a bullet strays away from the flight path, without some sort of external influence, it is going to continue off of that flight path. And to further my dilemma, if this phenomenon does indeed exist, I'm going to have to know "why"?!!!

Cheers,

Bill

 

[azimutha]

Re: Let's talk about dispersion...

One of my scopes doesn't have range markings on the parallax knob. Some people have complained about this - enough to get the manufacturer to go to markings. But I've never thought of asking for an upgrade. Adjusting until, as one SH member once put it, "the reticle appears to be plastered on the target" and moving your head around while looking at the target is the way to assure the scope is parallax-free.

 

[jrob300]

Re: Let's talk about dispersion...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: azimutha</div><div class="ubbcode-body">One of my scopes doesn't have range markings on the parallax knob. Some people have complained about this - enough to get the manufacturer to go to markings. But I've never thought of asking for an upgrade. Adjusting until, as one SH member once put it, "the reticle appears to be plastered on the target" and moving your head around while looking at the target is the way to assure the scope is parallax-free. </div></div>

Exactly. I've solved accuracy problems for guys that think those numbers are like a rangefinder. "But it said 100 yds!?" I actually prefer SF knobs with no markings.

John

ETA: But... we digress, and we're not helping Bryan very much... Sorry, Bryan.

 

[260shtr]

Re: Let's talk about dispersion...

I have this problem with a 7MM REM Mag, 700 action, 4-16X50 Nikon Tactical, Broughton 26" barrrel, Berger 168 VLD. Typically 1 MOA at 100 and 200 but will do 1/2 MOA or better from 400 to 700 (farthest I've tested it).

I will try to get out this weekend and reshoot 100 and 400 yard paying particular attention to parallax. And report back.

 

[hibc]

Re: Let's talk about dispersion...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 260 shooter</div><div class="ubbcode-body">I have this problem with a 7MM REM Mag, 700 action, Broughton 26" barrrel, Berger 168 VLD. Typically 1 MOA at 100 and 200 but will do 1/2 MOA or better from 400 to 700 (farthest I've tested it).

I will try to get out this weekend and reshoot 100 and 400 yard paying particular attention to parallax. And report back. </div></div>
This is probably a barrel twist issue, the twist maybe too fast or too slow for this bullet.

 

[GuinnessNM]

Re: Let's talk about dispersion...

To unambiguously demonstrate this effect one would have to simultaneous shoot the 100 yard and 200 yard targets. One target in front of the other (corrected for drop), same bullets through both targets.

 

[Lowlight]

Re: Let's talk about dispersion...

I would bet it is more a shooter based psychological effect than a physical one within the system. I have heard about rounds going to sleep, and all that entails and I think it comes from the 168gr vs 175gr visual at 100 yards.

Most rifles will shoot crazy good groups at 100 yards with a 168gr SMK when compared to a 175gr round and while they will appear to be tighter up close, at distance the 175gr naturally shines.

Personally I think it's because people can see the shots at 100 better and will hyper focus on the targets and blow shots, where they can't see the shot groups at distance and in effect shoot better. It's that old "refrigerator group" where they see they have a great group going by shot 3 and then shot 4 is completely blown, after the pressure is off shot 5 goes back into the original group. What happens they see they are doing well, then will shift their body and attention and tell themselves not to screw it up, where they immediately go and screw it up. Shooting at 300 or more yards you won't see the shot group, so psychologically you just continue to shoot normally so they tend to not mind fuck themselves.

At least it is my take on it, because of the barrels we use and the fact from one barrel to the next the tooling will get dull, I can see a stability issue, but I bet it is rare compared to shooter induced problems.

Shooting is more about thinking, we'll do some crazy things in our head that will transfer to our hands and effect our downrange results.

 

[ssgp2]

Re: Let's talk about dispersion...

My impression of what is happening in certain cases, is that the same target is used at 100yds and over.

Making the point of aim smaller at longer distance and therefore the shooter will be more careful in his aim.

 

[AQC440]

Re: Let's talk about dispersion...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ssgp2</div><div class="ubbcode-body">My impression of what is happening in certain cases, is that the same target is used at 100yds and over.

Making the point of aim smaller at longer distance and therefore the shooter will be more careful in his aim. </div></div>


AHh the good ole' "aim small, miss small" principle!
I have often wondered this myself or perhaps there is less perceived movement at the longer distances giving you more confidence when breaking the shot...Of course one could argue the fact that more concentration and aiming harder, brings on muscle tension and stress that would push the shots out regardless. We'll see!

 

[TiroFijo]

Re: Let's talk about dispersion...

I think it <span style="font-style: italic">may</span> be shooter error, like LL said.

With one of my rifles and a 16X fixed scope I consistently shoot great groups at 100 m, when I try to duplicate the groups (in MOA) at 200 m it is much harder, and then at 300 m and beyond (where I cannot see the bullet impacts anymore) I shoot great again. In this case, no doubt it is me...

 

[MikeeBooshay]

Re: Let's talk about dispersion...

Again, apologies for not helping Mr Litz much,but offering the following:

I think it is more of a shooter problem, most of those crazy groups, the 100 was shot first, then the 300. Similiar to LL's testing for cold bore, it is possibly a case of cold shooter.

I have had the phenomena on a R700 custom, 1/11 twist 300 WM, Ziess scope, MD reticle, using 180 grain barnes TSX. Fed Premium factory ammo. This is my usual hunting configuration, I will try that again next time at the ranch. Next time, I'll start at 300 and go to 100 second. Paper only, no spotters, no looking thru the scpotting scope either. No Shoot n See either, without that, I won't know the groups till I go down.

That refrigerator group GRRRRR! Was shooting with Jacob at RO, 3 in one hole on target, he says "You know this is the one, right?". And of course, #4 was out, #5 was in. You have to laugh at it, because it IS very predictable.

 

[Greg Langelius *]

Re: Let's talk about dispersion...

I think Bryan's correct, and would suggest that when such angular decreases occur, the distance at which they are smallest is the true distance at which the parallax is corrected, and also suggest that this distance will change every time the shooter re-'adjusts' the parallax.

Parallax adjustment isn't a 'set to the number' process, but an interactive one.

Maybe it should be, but it seems it seldom actually is.

I think that's because while parallax and distances have a linear relationship, the practice of scope makers to seize on this and combine the focus and parallax adjustment can lead to overconfidence and unrecognized error.

This because they often get the correlation wrong at the factory. It one of those issues that a cheap scope is a lot more likely to have than a more expensive one, but probably no make/model is immune.

Focus is obvious, parallax adjustment isn't, and when the factory correlation is off, a good focus will practically always mean a bad parallax adjustment. Under such circumstances, a properly adjusted parallax may mean having to sacrifice a crisply focused image.

I think this is a lot more common than most shooters understand, and that parallax is probably the most common cause of shooting error. Probably more than half of all shooters suffer from this issue at least some of the time.

They do it because they think the distance numbers on the scope's focus adjustment will give them a good parallax correction at the same time. If my thinking is correct, theirs isn't.

The nod/wag technique, to check parallax, is essential in my thinking; and folks who don't do this may be getting more effective dispersion than their rifle is producing all on its own.

Greg

 

[jrob300]

Re: Let's talk about dispersion...

Very well stated, Greg. I couldn't agree more.

John

 

[260shtr]

Re: Let's talk about dispersion...

Took the 7 Mag out today. It was the 3rd rifle to be fired. Of the first two 5-shot groups my 260 shot a .367. Next the 6.5X47 shot a .467. The first 3 out of the 7Mng went into .437, the last two were .125 to the right of the main group 1 inch. I think with the 7 Mag it is a positional problem or right hand grip problem. The rifle will shoot, I have proven it to myself at long range. It takes more concentration to shoot 100 yards.

I will be doing more 100 yard practice now and pay close attention to the fundamentals.

 

[Bradley]

Re: Let's talk about dispersion...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">

The nod/wag technique, to check parallax, is essential in my thinking; and folks who don't do this may be getting more effective dispersion than their rifle is producing all on its own.

Greg </div></div>

I agree. Being that we are human makes it tough to get the eye in the EXACT same place behind the scope time after time. I've always used the nod technique to adjust the parallax when shooting for groups, working up loads, or when time allows in a match. Another thing that I've learned over the years is to turn the parallax to infinity and start the adjustment process. If I pass the sweet spot on the way down, I don't just back it up to where there is no movement in the reticle, I turn it back to infinity again and start over. I do this because I've experienced what I think maybe a certain amount of backlash in the parallax adjustment of a scope I had a few years ago. Since using this technique, I've had to go buy another refrigerator.

As far as the "bullet going to sleep" theory goes, I just can't see it. A well accomplished shooter was trying to explain his take on it a while back, and though I understood some of the points he made and witnessed not so good groups at closer ranges, and excellent groups at distance. I find it hard to believe.

 

[KQguy]

Re: Let's talk about dispersion...

I alway's shoot a better MOA at longer range,than I do @ 100yds.I know for me it's all mental,I am alot more relaxed the farther out I shoot.When I shoot 100yds,I feel like I alway's need to have all the holes touching,so I alway's put more pressure on myself.When I am shooting longrange,I know that is not expected,so I don't care as much,and end up shooting better.