Thread: 3 shot groups are useless!

Small dot on big plate=more info.

https://youtu.be/-ZpYFSqukhs?si=YmAuM-tKU95rU-Ja
From 14.48 in this video there's a good point made: if you adjust you POA based on only a few shots you can end up screwing your accuracy. Because when you adjust your scope you're adjusting your group's POI, not the last shot's POI.

He was making another point here (are mils really not fine enough to adjust vs MOA?), but he also illustrates this discussion quite well.

Identify your target beyond all doubt because you never miss (right?) and I'll be missed.

I video all my shots, to log each shot poi and especially to catch any misses. Missed shots usually mean a problem with the system and I really want to diagnose and find it.

My Sunday arvo shoot deciding what components to use in the 6CM. All shot at 302m. My 223 and 6.5prc were shot to use time cooling between 6cm groups.
And to verify their loads against the new garmin chronograph. All are lightweight hunting rifles.



What an awesome piece of kit the garmin chronograph is!
223 group is the first shots of the day 1st cold/fouler is center plate.

Old forum gimp.

That's dismaying news.

I lay prone with bipod and a bunched dog blanket under the heel of the stock.
Fired the bottom 3 shots. Stood up and had a pee. Fired the top 3 shots.

Sorry only 6 shots but Im not at home and conserving ammo. And no tape measure.

.223 M7 and 52 grn Targex.

What size are the sticky rectangles ?

Originally Posted by gimp

What size are the sticky rectangles ?

Look about .75"

Another 3 shots might have blown the whole thing apart.
I will still do the 10 shot thing when I get home.

On the short axis?

It does nicely demonstrate the variation you should expect with 3 shot groups in terms of the extreme spread - even with only 2 groups, they are quite different in size. You should expect variation of 70% +- from the average (if the average is determined over a meaningful number of 3 shot groups)

It is difficult to determine whether there is much of the expected variation in MPOI visible between these 2 groups (remember they are still a very small sample) without a reference dimension to measure against (e.g. grid paper)


More data needed to determine what it tells us about the MPOI or precision of this rifle system. Initial signs are that it isn't immediately obviously bad.

Originally Posted by gimp

It does nicely demonstrate the variation you should expect with 3 shot groups in terms of the extreme spread - even with only 2 groups, they are quite different in size. You should expect variation of 70% +- from the average (if the average is determined over a meaningful number of 3 shot groups)


More data needed to determine what it tells us about the MPOI or precision of this rifle system. Initial signs are that it isn't immediately obviously bad.

I truly thought the top group would be like the bottom one.

Originally Posted by Tahr

I truly thought the top group would be like the bottom one.

well technically....if the middle hole of top group was the aiming point/point rifle sighted in to hit...
and the bottom hole of bottom group was same
both groups have no other holes further away from point aimed at LOL.
one has two other holes slightly high..the other one slightly high and one slightly left...
statistician can make any data suit agenda

Originally Posted by Tahr

I truly thought the top group would be like the bottom one.

The idea that a rifle will group consistently the same size or mean point of impact with 3 shots is an unrealistic expectation - there will inherently be variation.

We can't get around the reality of statistics - it describes the nature of the world as it is (to a degree - all models are wrong, but some are useful).

The question is the degree of inconsistency, which obviously is dependent on the quality of the rifle/shooter system. No matter what, more data rather than less is required to confidently make statements about it. This is, of course, irrelevant for hunting at conventional ranges as our targets are large, results are rarely recorded and critically analysed, and precision is relatively unimportant compared to shooter proficiency (but shooters can waste a lot of time chasing unrealistic expectations based on insufficient data - gather more data initially and have more confidence, shoot less at paper and more at animals in the long run)


Rather than write a post about it myself, this article is reasonably good


https://www.bealeinnovations.com/stats-3shotgroup.pdf

Originally Posted by Tahr

I truly thought the top group would be like the bottom one.

Clearly you shoot better with a full bladder.

Originally Posted by chainsaw

Clearly you shoot better with a full bladder.

A sniff of the fog in the air gives me a full bladder Its an age thing.