Thread: 3 shot groups are useless!

three shot groups is all i can afford... betcha if i do my part dead critter....

Ok.....I can buy that...... So if I was to zero at 100 with X number of shots,The confirm at 250-300 with another X number of shots...I will have satisfied both criteria.... Because I seldom shoot past 300m 350 at most..by eyetrometer....that is more than good enough for what I do. So I will respectfully disagree with original assumption/ presumption/statement and contend that rather than useless...they have some use/merit.

About 2 or 3 times a year il shoot a few rds at 300 n 400yds,just to make sure my scope n rifle are on song.But most deer are inside 320-330 yds so I have no problem smacking one over out there at distance if the shot is on.

Originally Posted by Barry the hunter

I think this subject has run its course young hunters there is nothing wrong with a check zero of a rifle that has been previously zeroed just before you go for a hunt- that is all I need to know - my 788 first dry fire will be slightly high and left no more than 1/4 inch at 100 it has done that for 40 years next will be spot on - does not miss a beat - why waste another 20 rounds to tell me any different - and besides after 5 I dont want to do any more any way - we are not olympic shooters - for a 10 round group to mean anything all our faults need to be eliminated - fatigue - flinch - hold - comfort - precision - trigger let off - most on here are not target shooters to be able to do that reliably - so it is in some ways not a meaningful argument theres to much shooter error - just zero your rifle and check it regularly - held me in good stead last 50 years - and thats my last post on this because 3 shot groups its not an argument for most kiwi hunters - leave it to the target shooters where it belongs

You keep arguing against a position Noone is holding

no

Originally Posted by Barry the hunter

no

It's an observation, not an instruction. You'll probably be much happier if you don't

We use shorthand/abbreviations/approximations in language all the time e.g. “about 20 minutes away”, “not far from here”. This way of speaking prioritises rapid communication of ideas over absolute precision. This language is both common and useful; however, may not be fit for purpose when a higher level of precision is demanded e.g. communicating an important dimension on a building design.
To my way of thinking, this concept is parallel to the discussion of firearm accuracy and precision. If you want to know your true cone of fire (i.e. precision) or your true zero (i.e. accuracy), you will need a sufficient sample size to give you a proper representation of this. A relevant question then becomes - do you need to know your ‘true’ cone of fire or your ‘true’ zero?
I think it has been established, that in many cases the answer is no (i.e. when shooting deer-sized targets at moderate ranges). Therefore, in many cases an approximation (e.g. the three shot group) will probably suffice. However, if your demand for precision is high (e.g. longer range/smaller target); the details naturally become more important. It also follows that if your true cone of fire is small to begin with (i.e. you have a high level of precision), every sample is inherently closer to the mean so to speak, so again a three shot group may actually be a reasonable representation of that system.
It seems part of the debate occurs when people perceive any discussion of larger sample sizes as some sort of prescription you have to follow, rather than seeing it as simply a statistical fact about increasing resolution with more samples, and the inherent problems of small samples.

Originally Posted by Longrun

Yes, there is definitely room for more to be known from larger group samples. Here's an easy to read article that I found more palatable than gimp dogma.

https://www.everydaymarksman.co/mark...fle-precision/

Yep, but his persistence (and that of others) has made me a better equipped hunter...who is now thinking about a well setup 223 to meet most of my needs.

Persistence is one description

Originally Posted by Longrun

Persistence is one description

Thats a bit disingenuous. gimp and tentman have provoked some thoughtful discussion and I think changed the 3 shot perspective for many of us. Lots over my head but I trust gimp to have been steering the conversation in a direction that everyone can benefit from.

All can be achieved with 10 mins of easy reading without the accompanying condescension.

Originally Posted by Tahr

Thats a bit disingenuous. gimp and tentman have provoked some thoughtful discussion and I think changed the 3 shot perspective for many of us. Lots over my head but I trust gimp to have been steering the conversation in a direction that everyone can benefit from.

I actually want everyone else to shoot worse and less successfully.


Right, enough about my many and various personal shortcomings, let's look at some 3-shot groups. Last week.


This is a pretty normal data set. Standard T3 7mm08 with a handload, leupold scope, expert shooter (much better qualifications than me), off the bench at 105m. No wind to speak of. Getting a zero for <300m hunting.


Whole target:



First 3 shot group - 0.87 MOA - adjusted up 1.0MOA and right 1.5MOA after this.


Second 3 shot group - 1.08MOA - adjusted up 0.5MOA and right 0.5MOA after this


Third 3 shot group - probably good enough for the purpose.


We can use the data from this exercise to undertake some analysis. I adjusted all the shot for their position to have a common point of reference - translating groups 1 and 2 by the total adjustments to overlay them on group 3.

This analysis does make the assumption that the scope is functional. If the scope has a relatively massive error, like 10%, then the analysis is still broadly correct. If the scope is total junk and just does not track at all, then the analysis might be questionable.

Here's what we get.

Precision:

The rifle shot 3x 3 shot groups averaging 1.09 MOA. Pretty good. The combined group of all 9 shots is 71.5mm, or 2.3 MOA.
The mean radius of the 9-shot sample from a common point of reference is 19.8mm with an SD of 11.9mm (+- 9.1mm @ 95% CI)
This mean radius means that the total dispersion of the rifle is around 82.3mm (2.7MOA). (44 - 120mm @ 95% CI)


Accuracy:
The MPOI of all 9 shots is at +1.8mm (+- 18.8mm @ 95% CI) for windage, and +2.8mm (+- 15.3mm @ 95% CI) for elevation.
We can be highly confident that it's zeroed within 2 clicks in each direction. That's good for the intended purpose. We cannot be more confident than that.

The mean POI of group 1 (adjusted) is 17mm right of the 9-shot MPOI, and 13mm high.
The mean POI of group 2 (adjusted) is 13mm left of the 9-shot MPOI, and 13mm low.
The mean POI of group 3 (adjusted) is 3mm left of the 9-shot MPOI, and almost pefect for elevation.

So one of the 3-rnd groups accurately matches the best estimate we have of the true MPOI within 2 clicks in each direction, the other 2 are about 2 clicks off in both directions.


This is a handy example of getting a zero that's suitable for hunting at conventional ranges using 3 shot groups with a rifle of pretty average precision. Very normal situation. We can pool all the data and have an understanding of exactly how confident in it we can be, and for what.


You'll notice, @Micky Duck, that 2 of the 3x 3-shot group MPOIs are far more than 20mm apart - you indicated that you've never seen this in 50 years, but this is not unusual with systems with average precision and small samples.

It's a dead deer....

Originally Posted by Micky Duck

It's a dead deer....

did anyone say it isn't?

Look ive read all 20 pages . Im not stupid ( I don't think ) . I just don't get it. if I shot that group above I'd be suicidal . I shot a couple of 3 shot groups with handloads last week. Both were touching . I went hunting and shot a couple of deer. What am i missing ?