Cone of Accuracy?

[rckendall]

A couple years ago, probably, I read an article explaining the probability of hits at different places (scoring rings) based on the accuracy of the rifle/load combination (the cone). It made good sense to me and I would like to find and re-read it. I have searched but I am probably not using the right verbiage.

Can someone please steer me in the right direction?

Thanks,
Richard

 

[mike mccormick]

Sounds kind of like factory lot testing on rimfire match ammo. Eley's tests show percentages of where shots land on target like that.

 

[ShootDots]

I remember reading either that article OR a very similar one. I don't remember where I read it>>>>but it seems to me, that it might have been from Brian Litz. This was more than a "couple of years ago" >>>maybe 5 or so. Check out any articles written by Litz>>>it may be in there...

 

[MikeMcCasland]

I think you're talking about WEZ from Applied Ballistics:

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[Snozzberries]

I had a long conversation with a friend about this. How do you determine how accurate a rifle is? Shoot a single 3 round group? Shoot a 5 round group? As you increase group size, you increase the chance your group will grow in size. What if you shoot multiple groups? Do you measure the best group? The worst group? Average all of them?

What's the best gauge? Lots of 3 shot groups? One single 50 shot group?

It's really a statistics problem. Perhaps rifle's follow bell curve.

http://www.the-long-family.com/Group%20size%20statistical%20analysis.pdf

 

[tsyarnall]

I do believe that, at a certain point, the heating of the barrel will cause it to twist and droop. Part of this from the warming of the metal and the pull of gravity. Part from the different thicknesses of the barrel (rifling or lack there of). So, as the number of rounds increase, the results from heat and gravity will likely not remain constant.

Scott Y

 

[mac86951]

I had a long conversation with a friend about this. How do you determine how accurate a rifle is? Shoot a single 3 round group? Shoot a 5 round group? As you increase group size, you increase the chance your group will grow in size. What if you shoot multiple groups? Do you measure the best group? The worst group? Average all of them?

What's the best gauge? Lots of 3 shot groups? One single 50 shot group?

It's really a statistics problem. Perhaps rifle's follow bell curve.

http://www.the-long-family.com/Group%20size%20statistical%20analysis.pdf

Problem with statistics, there's never enough data. I'm guessing after 10k rounds we'll know how accurate a 6.5x284 was. Emphasis on was.

I think we've developed our own methods of applied statistics to judging rifle accuracy during load development meaning there isn't really a "best" gauge; i suppose that depending on application, I'd argue that 5 5-shot groups would be a good place to start for comparison, but I might hesitate to shoot that from a .50 if I'm paying for ammo. Take your intended shooting discipline and I bet you'll find a competition oriented on something similar.

-Mac

 

[rckendall]

I think you're talking about WEZ from Applied Ballistics:
View attachment 1275058

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Thanks for this. I'm not sure this is the one I read before, but this definitely has the right slant on the subject.

Also the one by the Long folks was interesting and I will try to digest from them both.

This came up when a buddy and I were shooting a 12"x20" silhouette target at around 1000 yards. With a zero not actually determined yet and a shot too high, we would adjust the scope for a lower impact. Then we might have a shot too low, and another scope adjustment was in order. The same was happening with the horizontal shots/scope changes.

I began to think that we might be better off to not change the scope until more shots had been fired. Then I remembered the article I'm referring to and knew that I should read it again.

Thanks for the responses and keep them coming.
Richard

 

[RegionRat]

https://appliedballisticsllc.com/wp...the-Maximum-Effective-Range-of-Small-Arms.pdf

https://precisionrifleblog.com/2015/06/09/how-much-does-it-matter-overall-summary/

https://precisionrifleblog.com/2015/04/15/how-much-does-group-size-matter/

If it wasn’t one of these, maybe it was one of the linked articles.

 

[DaveTooley]

Thanks for this. I'm not sure this is the one I read before, but this definitely has the right slant on the subject.

Also the one by the Long folks was interesting and I will try to digest from them both.

This came up when a buddy and I were shooting a 12"x20" silhouette target at around 1000 yards. With a zero not actually determined yet and a shot too high, we would adjust the scope for a lower impact. Then we might have a shot too low, and another scope adjustment was in order. The same was happening with the horizontal shots/scope changes.

I began to think that we might be better off to not change the scope until more shots had been fired. Then I remembered the article I'm referring to and knew that I should read it again.

Thanks for the responses and keep them coming.
Richard

One shot does not show POI at any range.

Know the accuracy potential of your rifle. One shot can be anywhere in the potential group. Then factor in the variables from atmospheric changes. You'll end up chasing your tail.
If you get a big miss at distance make a coarse adjustment after the first shot.
Then engage your brain and shoot a couple of shots before making any scope adjustments.

When I'm shooting a 1K BR match I always shoot two sighters as fast as I can at the end of the sight in period. Then adjust to the middle of those two shots. That's with a rifle capable of shooting .4 MOA or less at 1K.

 

[rckendall]

https://precisionrifleblog.com/2015/04/15/how-much-does-group-size-matter/

If it wasn’t one of these, maybe it was one of the linked articles.

Yeah, That's the one!!! Thanks so much. I'll definitely save it this time in-case I ever want to read it again.

For me, it's back to load testing at 100 yards. I had two lots of handloaded ammo and one shot well and the other not so much? It's been fun and the wind reading lessons are soon to be tackled.

Thanks again,
Richard

 

[rckendall]

One shot does not show POI at any range.

Know the accuracy potential of your rifle. One shot can be anywhere in the potential group. Then factor in the variables from atmospheric changes. You'll end up chasing your tail.

I agree 100%. Chasing my tail was what I experienced with the poor performing ammo I had. When I went back to the good ammo, I had hits again.

 

[dnellans]

Since I've started doing my own barrels (large thanks to everyone on this site) I've been nerding out a lot more on group sizes since I want to now test both my shooting capability as well as my skills on the the lathe and workbench. Here is some food for thought on a practical experiment I did in July.

The setup is that I wanted to really test how much my group sizes and zero "shift" in a rigerous manner - so I took what is my PRS match load (6 BRA, 109 hybrids) and shot two 5 shot groups at 100 yards, every week for -4 weeks- over the course of July (usually about 9:30 am morning, chosen on the better weather of wed/thurs). Gunsmithing is by me and shot off a harris front bipod and fancy rear sandbag (gamechanger) that I recently moved to using with a different hold technique.

I'm a statistical guy so I looked at both the ES and the Mean avg in group sizes to see how it changed versus what mean to ES would be projected by the literature. Groups ranged from .277-.396 with a mean ov .318 moa and a SD of .042.

At first glance I was surprised at both how consistent they were and how little the zero appeared to shift, no group was centered outside of a .1mil scope click adjustment. But when you put it into excel you realize that the largest group .396 is almost 40% bigger than the smallest group, thats a lot.

If you look at the low and high group sizes at 2 or 3 SD out, for me to have confidence that a new load, or barrel is shooting better than this (since clearly I as the shooter can say I'm capable of shooting low .3's now) I would have to shoot groups that are in the low .2's or high .1's.

I could chase a load a long time in the .2's and it might not really be meaningfully different than my current load. Plus, without moving to flat back bullets, a f-class front rest, benchrest style rear bag - how do i know its not me that is not limiting the varience. After all, its a harris biopod and a rear squeeze bag!

Here is the raw data that might be of interest to someone one day.

 

[RegionRat]

So @dnellans , what did you conclude about POI shift over all the sessions?

Are you cleaning between sessions, or shoot foulers?

Did you track MV?

Did you track weather?

 

[dnellans]

POI shift was small enough i couldn’t even adjust for it but no two groups would have stayed within .3’s if i over lapped them. do think getting on and off the gun and/or parallax was as big a diff as anything else.

There is this thing in PRS shooting where you see guys show up and checking zero and often adjusting it. hell, i’ve done it too thinking something must have shifted.

but if four range trips to the same spot, same direction, same time of day, all put the groups within .25 moa of the center (and these groups are small enough they have a good center) then zero shift simply doesn’t happen on my gun. i’ll probably never check zero at a match again and just go straight to distance and validate it hits.

MV - i didn’t chrono each time, but i did before and after and it remained “the same” at 2890. SD 3-5, ES 10-12 is pretty typical for me with this gun/load.

no cleaning between any of the groups or even range sessions. no foulers or cold bore shots outside the groups either, though i do foul the gun with a few shots after cleaning normally. i didnt see any pattern that the “first” shot each week or in each group of 5 was the one outside the group, or anything like that. it did seem “random” which shot was the laggard in the group.

since that test i actually took the rifle to a match without cleaning it, so it’s now at 300 rounds without cleaning and this week i’m going to shoot one last group with it to see if it’s opened up or not. then i’ll clean it well, foul, and see if the same load still shoots.

if you don’t test this stuff, you never know if it matters.

weather wasnt tracked in detail but if you look at the “number” on each group, that was the order i shot them in, 1->8 and surprisingly no week is better or worse than the other and neither the first nor second group was always better each week. i’ll take that to mean weather was close enough to not really matter.

 

[RegionRat]

if you don’t test this stuff, you never know if it matters.

Profound statement!

And nice post. Thanks for sharing your work. Sounds like your effort is paying off!!!