Thread: Obtaining more information from your groups - overlaying groups

We have established that if you wish to make accurate statements about the precision or mean point of impact of your rifle system, then larger quantities of data are required than can be reliably obtained with the individual 3-5 shot groups that many people used to commonly shoot. Note that purpose here - making accurate statements about the precision/MPOI of the system. If you want to tell me this is irrelevant for normal hunting use: you are correct, you can stop reading and close the thread now.

The purpose for collecting more data is to have a better understanding of where your first shot will fall in a future scenario. A rifle system does not put every shot in the same place. It produces a cone of fire, and any shot in the future may fall anywhere within the circle described by that cone. 3 or 5 shots taken alone do not reliably tell you enough about that cone to accurately predict where a future shot will fall. This is well established and demonstrated. The average extreme spread measurement of multiple small groups doesn't give you information about the relative position of each shot and as such, is less informative.

I've developed a spreadsheet tool with tabs for overlaying up to 3x 10 shot groups, 6x 5 shot groups, and 10x 3 shot groups, to give a 30rd aggregate for each. This allows overlaying of multiple smaller groups and extracting information from every shot to get a more precise measure of the precision and mean point of impact of your system, if you don't want to shoot 10-shot strings on the same aiming point at one go.

This spreadsheet will give you:

- A visual overlay (scatter plot) of where all your shots fall across multiple groups
- A calculated mean radius value, to give a more accurate measure for the precision of your system
- A calculated mean point of impact so you can get a better zero.

It can be obtained at: https://filebin.net/x3rj8yovx6sd0aqu

INSTRUCTIONS:

Fire up to 3x 10 shot groups, 6x 5 shot groups, or 10x 3 shot groups, OR use previously fired targets
NOTE: All shots must have a common fixed point of reference (point of aim) - there can be no sight adjustments between shots

Use the Hornady Group Analysis App (or Ballistic-X or other group measure apps) to obtain the X (windage) and Y (elevation) values of each shot


Enter these into the relevant columns in the spreadsheet



All the fields and the scatter plot will auto-fill. The scatter plot is "corrected" to centre all shots around your mean POI.




So, if you shoot a series of 3 round groups like this, which are individually not very informative - you can now obtain more information from these.



I've already shared an earlier version of this with @Tentman, @flock, @McNotty, @zimmer

I would be interested to see other's results if anyone has a play.

I’m working on it, don’t get out much. Took a guess from load development target (only had photo) and dialled down 2 MOA and shot this group before heading out to chase some bunnies. Cheers for the spreadsheet. Got the updated one.
I still think I’m adding some noise to the groups with my shooting. Rushing a bit and also factory barrel possibly throwing a few at end with heat. Time will tell when I can sit down at range and take my time.

That looks like great precision for a factory barrel to me. What's your setup ?

I guess i do a similar thing but without a computer. I use the same target but keep masking it up and measure it with a ruler. The target is on a dense piece of cardboard so makes neat holes and you get neat holes in the masking tape as well.

Originally Posted by gimp

That looks like great precision for a factory barrel to me. What's your setup ?

Mauser M18 22” barrel - 223
Burris Signature 3-15
Sako brass
40gr Vmax
BM2 (max charge)

Fair bit of heat mirage on the last three shots. Will be interesting to see if it’s the nut or that’s just how it shoots

Interesting thread, and hopefully I can contribute next time I get the range.

I've wondered at times if 3 x 10 shot groups would yield the same results as 10 x 3 shot groups (especially across different sessions). There seems to be a certain set of skills involved to maintain consistency while shooting larger groups (excuse the pun), to avoid shooter fatigue, manage barrel heat/mirage, and sometimes to overcome discouragement when you start to see a group open up as put more rounds into it. At the other end, there are what I guess could be called "cold shooter" effects - maybe these get evened across a larger group?

I've posted this image before, however seemed relevant. Interestingly the first three shots were close to the central X (approximately 1/2 moa or less) and then opened up from there.

Most of what is perceived as "shooter" effects or groups opening up from "barrel heat" is demonstrably just groups filling out with more data. I have fired dozens of groups of various sizes from various rifles over the past year and when you get larger samples the perceived effects just go away - you just get a real picture.


Groups will (almost) ALWAYS get larger with more shots. You are just building a more true picture of the actual distribution of shots that the rifle system will produce.


Here's my 2x 10rd groups from yesterday with the factory 73gr ELD overlaid using this tool - they just fill out into a nice rounder picture of what the dispersion of the system actually is.



Mean radius 0.068MRAD - I should expect that 95% of shots I'd fire from this system would fall inside a circle of diameter 0.28 MRAD or thereabouts. So I can expect to reliably hit 0.3MRAD targets IF I can get perfect zero, perfect adjustments for range/wind, don't have excessive vertical spread at the relevant range due to velocity variation, etc - and I don't make any egregious shooter errors in the field.

Group extreme spread, of enough shots, give you a rough relative index of whether a rifle system is more or less precise than another. Mean radius gives you that, and a predictive tool for what size targets you can expect to hit.