Thread: Getting good data from 3 shot groups

Following on from this thread https://www.nzhuntingandshooting.co....llenge-119262/ I've been giving some thought as to how to best use 3 shot groups / minimum rounds to get a very precise zero.

So a very quick trip to the range today - I fired 13 shots and gained a heck of a lot of very usefull data, certainly enough to shoot to at least 500 or so with a lot of confidence. To achieve the 500 confidence you really need a scope of known dialing capability, old or very cheap is probably gonna disappoint.

So I fired 13 rounds total, shooting at 3 aiming points. Shooting was done "round robin" so one shot at each aiming point rather than 3 all at once at the same aim point. This rifle was already zeroed but had been shooting horribly (like 2+ moa) so it was deep cleaned for this test . . . So a cold/clean bore shot is included.

Here is a picture of the target after 9 rounds, at this stage I have three groups each of 3 shots.



This rifle is shooting pretty well and it's tempting to call it done but for the sake of a few more rounds we can get a lot more info by firing 4 more rounds and converting two groups to five shots.



The analysis is in the photo but I'll add some comments soon.

The average of the 3 shot groups is 0.6 MOA. Brian Litz and other ballistic experts tell us that a 3 shot group will "grow" by about 1.25 if we convert it to 5 shots. In this case my 5 shot group average is about 1.2 MOA which is a good bit over that.

In this case there's a flier, and it's tempting to call it a "pulled shot" but wether a flier or pulled it's data, so its included. And when you're out on the hill I guarantee you'll have more rather than less pulled shots (maybe you won't register them, deer are big targets, even rabbits are nearly 2 MOA at 100M).

The three groups in this case make a pretty consistent call for a minor (one click down) adjustment to zero but if the groups were bigger or less consistent, the the ATZ becomes even more usefull in sorting out how much to adjust. If the 3 shot groups were much bigger I'd convert one of the 5 shot groups to 10. Again Brian Litz tells us that a typical 3 shot group will grow by 1.85 as it's raised to 10 but the ATZ functions use of Mean Radius uses the data from all shots to give us a very precise adjustment. These particular 3 shot groups would indicate that this rifle is actually about a 1.1 MOA rifle ( and I'd say that's generously in its favour, it shoots better than it's usual average with this load).

Are 3 shot groups useless? Well maybe not if used to their best advantage as opposed to using them to make claims about the accuracy of a particular rifle aka "my Tikka shoots half MOA all day".

I perhaps should point out that this is a 223, and I wouldn't be shooting deer or other game at 500 with it, but 280- 350 might be doable in ideal conditions. And yesterday at the range a Tikka 6.5 PRC did indeed shoot two consecutive 100M groups of 0.4 and 0.5 MOA (5 rounds in each).

I wanted to try your data out and get your thoughts. I plotted them as you shot them into three 3-shot and two 2-shot groups from left to right. Assumed 100yard and 1 inch diamond.


Overlaying the aggregates:


Then centering on aimpoint:


My first thought was I wanted centered on aim point for small data sets such as 3 shot groups, as this should negate the lack of true MPI from lack of individual group data. Then I figured if this was a long term analysis with many more groups added then centered of MPI would probably give the same result eventually but wouldn't be affected by zero changes.

Ohh I see you round robined it so my groups are out, however my aggregate treats them as individual shots. As to your original purpose, 13 shots to zero: one click down

Yeah so it's not a bad combined group at all. Or to put it another way....had I shot those three groups to check zero say three months apart...I would not have moved scope at all.

Originally Posted by Tentman

Following on from this thread https://www.nzhuntingandshooting.co....llenge-119262/ I've been giving some thought as to how to best use 3 shot groups / minimum rounds to get a very precise zero.

So a very quick trip to the range today - I fired 13 shots and gained a heck of a lot of very usefull data, certainly enough to shoot to at least 500 or so with a lot of confidence. To achieve the 500 confidence you really need a scope of known dialing capability, old or very cheap is probably gonna disappoint.

So I fired 13 rounds total, shooting at 3 aiming points. Shooting was done "round robin" so one shot at each aiming point rather than 3 all at once at the same aim point. This rifle was already zeroed but had been shooting horribly (like 2+ moa) so it was deep cleaned for this test . . . So a cold/clean bore shot is included.

Here is a picture of the target after 9 rounds, at this stage I have three groups each of 3 shots.

Attachment 289631

This rifle is shooting pretty well and it's tempting to call it done but for the sake of a few more rounds we can get a lot more info by firing 4 more rounds and converting two groups to five shots.

Attachment 289632

The analysis is in the photo but I'll add some comments soon.

What scope are you using?

Currently on this rifle is a Zeiss HD5 3-15 .

I know you’ll have your reasons for shooting round robin targets but this assumes the shooter has excellent positional shooting technique thus not affecting bullet strike. Indoor 22 target shooting often shows up poor technique which often shows on the target depending upon sequence that each target is shot on card. Same would apply at 100m/y I would assume, though to a slightly lesser degree. Just a thought.

Originally Posted by Tentman

I perhaps should point out that this is a 223, and I wouldn't be shooting deer or other game at 500 with it, but 280- 350 might be doable in ideal conditions. And yesterday at the range a Tikka 6.5 PRC did indeed shoot two consecutive 100M groups of 0.4 and 0.5 MOA (5 rounds in each).

Two of my Tikka's will shoot 5 shot .3 moa groups...my 223 is more .75. The ratio of really good Tikka barrels seems high...I have only shot big groups with the 223, need to get on it.

Originally Posted by woods223

I know you’ll have your reasons for shooting round robin targets but this assumes the shooter has excellent positional shooting technique thus not affecting bullet strike. Indoor 22 target shooting often shows up poor technique which often shows on the target depending upon sequence that each target is shot on card. Same would apply at 100m/y I would assume, though to a slightly lesser degree. Just a thought.

Interesting point I hadn't considered. As I understand round robin is supposed to reduce the effects of barrel heating. In the context of a hunting rifle that will be shot from many different positions maybe round robin is an advantage in that it reproduces the variability a shooter is likely to get in the field.

Originally Posted by Tentman

Interesting point I hadn't considered. As I understand round robin is supposed to reduce the effects of barrel heating. In the context of a hunting rifle that will be shot from many different positions maybe round robin is an advantage in that it reproduces the variability a shooter is likely to get in the field.

Barrel heating is pretty irrelevant in this scenario



The sampling design is dependent on the question you're trying to answer. If you're looking to establish a good mechanical zero, there is no reason to shoot multiple groups rather than just 1 larger sample, or to round-robin

Originally Posted by Hahn

I wanted to try your data out and get your thoughts. I plotted them as you shot them into three 3-shot and two 2-shot groups from left to right. Assumed 100yard and 1 inch diamond.
Attachment 289641

Overlaying the aggregates:
Attachment 289642

Then centering on aimpoint:
Attachment 289643

My first thought was I wanted centered on aim point for small data sets such as 3 shot groups, as this should negate the lack of true MPI from lack of individual group data. Then I figured if this was a long term analysis with many more groups added then centered of MPI would probably give the same result eventually but wouldn't be affected by zero changes.

Ohh I see you round robined it so my groups are out, however my aggregate treats them as individual shots. As to your original purpose, 13 shots to zero: one click down

You need a fixed reference to overlay groups as a composite. Apparent group MPI moves around a lot between 3 shot groups. Aim point is a good fixed reference point but the shooter cannot make sight adjustments between groups if wishing to overlay, unless they're known and accurate and accounted for.

Tentman what units are your "ATZ" recorded in

Originally Posted by gimp

Barrel heating is pretty irrelevant in this scenario



The sampling design is dependent on the question you're trying to answer. If you're looking to establish a good mechanical zero, there is no reason to shoot multiple groups rather than just 1 larger sample, or to round-robin

You're assuming I'm appealing to logic, I'm not, this is about belief!

Originally Posted by gimp

Tentman what units are your "ATZ" recorded in

CM.