3 shot group validity

I usually shoot 5-shot groups, but am most likely going to switch to 3-shot groups for testing. Try to reduce components expended when doing load development at first. As I get a better idea of what loads have potential, then I'll up it to 5-shots again while I tweak it. I'm more of a hunting guy than a competition shooter, so if I'm shooting around 1 MOA or less AND have adequate velocity to ensure bullet performance at my intended ranges, I'm a happy camper.
 
I'd like to chime-in here and share an interesting resource that I came across some time ago. I should probably give a disclaimer that this website is pretty heavy on the math terminology, but if you appreciate statistics then you might enjoy this read:

http://ballistipedia.com/index.php?title=Home

And this one too:

https://www.ar15.com/forums/ar-15/-/118-279218/?

I'll cherrypick a few interesting quotes to share here:

"...if you're shooting 3-shot groups or groups larger than 9 shots then you are wasting bullets." (from ballistipedia - Range Statistics)

"By the time we're looking at the average of five 5-shot groups our distribution has almost no skew." (from ballistipedia - Range Statistics)

And from the second article linked above:

"Ten shots are a more reliable indicator when it comes to predicting what a load is likely to do in the future... Three shots forming a tight cluster is nice to look at, but it is little more than an accident. Shooting three-shot groups to see how everything is working is essentially a waste of time and components."

So I think it's safe to say that 3-shot groups can help omit loads that are outright bad, but it might take a little bit more work to hone-in on a load that's actually good.
 
please note that the RIFLE and the shooting set up will have a huge affect on how many shots is statistically useful.

On an AR board, I supposed they are talking about tuning AR rifles. Here you are working with rifles that can range from 1/2 MOA to 3 MOA. When the rifle may not be all that accurate, increasing the sample size will help to prove what is working and not. Same would go with factory bolt rifles.

When using supports that can introduce error into your results, larger sample sizes will help eliminate shooter error

A rifle with MOA potential could shoot a 1/2 MOA 3rds group. Repeatable? Consistent? maybe not... so increasing the number of shots helps determine what the average performance is.

However, if you are working with purpose built 'accuracy' minded rifles with match barrels, bedding and ammo that have accuracy potential in the sub 1/2 MOA range, having a test load exceed that or meet the performance goals are both very telling on what load to use.

For example, when I am tuning a FTR rifle, I know it has to shoot 1" or better at 300yds to be competitive. I know where my node is cause I am using similar components. When I reach that performance with a reasonable number in the group, I move to further distance cause it is telling me all I need to know. These rifles are purpose built to be highly repeatable and consistent... and the set up allows for VERY consistent shooting. So as long as I don't make a shooting error, the set up will deliver.

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I am shooting at 250yds with my FTR rifle (308win chambering) I am holding center and there is a slight right to left wind that rises and falls. Which load do you think I should choose? and do you feel that the number of shots is enough to confirm that?

Jerry
 

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Well shot a bit yesterday with the two loads that showed promise. Both shot under .7 with five shot groups. For me I am happy as my goal is to hit an 8" circle at 500 yards and I think the load and rifle are capable with this set up. The gun has consistently produced .6 to .7 MOA groups at 100 and at 300 yards. Most likely it can do better but I think I will start sighting in at 500 and just have fun with it.

I am no competitive shooter lol.. so trying to tune the loads more may be a waste of components for me.
 
For what it's worth, I normally do my initial load dev with 3 rd groups by I shoot 2 of each load. I'm normally looking for a specific velocity range and obviously also tight groups but I also want the composite of both 3 rd groups to be tight/have the same poi.
 
powdergun said:
I know this is one of those old debates that has been beaten to death and yes a .5 MOA 10 shot group repeated ten times is definitive but my question is as follows.

Can 3 shot groups be used to exclude a load as not worth trying ? In other words if a load shoots 3 shot groups that are not what you want is that enough feedback to drop that load and try another.
Click to expand...

it can depend on the distance you plan on shooting - a so so group at 100 yards can tighten up at 200-300 or more - i would recommend trying the three shot group at various distances - when you shoot xnumber of rounds your barrel heats up and it will affect POA
 
powdergun said:
Well shot a bit yesterday with the two loads that showed promise. Both shot under .7 with five shot groups. For me I am happy as my goal is to hit an 8" circle at 500 yards and I think the load and rifle are capable with this set up. The gun has consistently produced .6 to .7 MOA groups at 100 and at 300 yards. Most likely it can do better but I think I will start sighting in at 500 and just have fun with it.

I am no competitive shooter lol.. so trying to tune the loads more may be a waste of components for me.
Click to expand...

The further you go, the more obvious the better load tune will be. Make up some of each load and go for it. I like to test in a sandy area so I can easily spot the misses. You will know real fast which load you want to stay with.

I just did a quick work up with a customers 6mm Creedmoor rifle which I have done a post for nearby. 170m got me to a load range that worked well. 5rds each at 700m and it was obvious which load he can start with. The difference at 170m is not much to speak of... at 700m, it was substantially different and easy to tell.

Good luck.
Jerry
 
Ever notice that 5 shot groups tend to be about 50% bigger than 3 shot groups? Guys should pay more attention to what their worst 3 shot groups look like, because they are going to measure out like the average 5s. 10s don't seem expand at the same rate over the 5s; which is telling me that at 5 you are beginning to get somewhere.
 
Mystic Precision said:
The further you go, the more obvious the better load tune will be. Make up some of each load and go for it. I like to test in a sandy area so I can easily spot the misses. You will know real fast which load you want to stay with.

I just did a quick work up with a customers 6mm Creedmoor rifle which I have done a post for nearby. 170m got me to a load range that worked well. 5rds each at 700m and it was obvious which load he can start with. The difference at 170m is not much to speak of... at 700m, it was substantially different and easy to tell.

Good luck.
Jerry
Click to expand...

People also need to keep in mind that the further out you go, the more variables and factors you bring into the tests. The effects of environmentals are amplified at distance, the further you go, the more amplified the effects become.

Now, don't interpret what I'm saying as never doing load tests at distance. But be mindful of all of the factors that are now being introduced that are out of your control but will have an impact on your testing. Once a load is established, it's always good to test things out at distance.

I'm personally an advocate of dialing in a load at 100 yards, where the external environmental factors are all isolated (same reasons for why we have a 100 yard zero). Establish a load with a tight ES/SD, that will deliver consistent ballistic performance across distance. A good shooting load at 100 yards will not fall apart at longer ranges, especially if you have good ES/SD.
 
I can remember one day at the range when we had to delay shooting because of fog. That was the only perfect day I can remember to test long range loads... just as the fog cleared and before the sun and wind kicked up.

It was absolutely dead calm and group sizes were crazy small for all of us on the base. We referred to that morning as a trigger pulling contest as scores were perfect across the board.

Unless you are testing long range loads under such conditions all you can really do is gusetimate the group within the group, but that is difficult to do.

If you ever get the chance to shoot as the fog clears and compare such a group to what happens the rest of the time, you'll see how much noise there is at medium to long range.

You can do a would have should have check on a shot to shot basis... or a post mortem... This is where you write down the scope setting... point of aim... and point of impact for every shot... then compare to condition changes to see if it was a wind read error or incorrect dope... or if you called it perfect... From that you can extract an idea of true accuracy... but you need to be pretty focused to figure it out. This is essentially how I've been plotting F Class scores for the past 20 years.

For those who dont trust your chronograph...

Accurate to 1/2 FPS... Got to get me one of these one day and test it.

 
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Bullets can stabilize after 100 yards so the group while not smaller may be better as measured in MOA

A 2 inch group at 100 yards is 2 MOA where as a 3 inch group at 300 yards is 1 MOA. Not tighter but a better group.
 
powdergun said:
Bullets can stabilize after 100 yards so the group while not smaller may be better as measured in MOA

A 2 inch group at 100 yards is 2 MOA where as a 3 inch group at 300 yards is 1 MOA. Not tighter but a better group.
Click to expand...

Except, a 2” group at 100 yards isn’t going to be a 3 inch group at 300. See above.
A bullet’s procession may dampen out slightly (this usually happens inside the first 20-40 yards) but it isn’t changing directions. Not without an outside force.
 
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If you watch this video, you might see why groups seem to tighten up at distance.

In the slow motion footage you can see the bullet is orbiting in a corkscrew path, but impacting in a fairly consistent place along the cork screw and printing smaller groups than the over all path.

The tighter group is coincidental, so the argument that a rifle can shoot better groups at longer range is not incorrect, but that does not mean the overall path of the bullet settled out. Move the target 10 feet and the impact could be somewhere else in the wider corkscrew path.

So it seems both arguments are actually correct... sort of.

 
Maple57 said:
If you watch this video, you might see why groups seem to tighten up at distance.

In the slow motion footage you can see the bullet is orbiting in a corkscrew path, but impacting in a fairly consistent place along the cork screw and printing smaller groups than the over all path.

The tighter group is coincidental, so the argument that a rifle can shoot better groups at longer range is not incorrect, but that does not mean the overall path of the bullet settled out. Move the target 10 feet and the impact could be somewhere else in the wider corkscrew path.

So it seems both arguments are actually correct... sort of.

Click to expand...

No. The “wobble” he talks about is procession. It’s the projectile pitching and yawing in either a decreasingly or increasingly stable pattern around its centre of mass. It does this on its predetermined trajectory. It does not change directions mid flight. The centre of mass is more or less on the plotted direction. The bullet itself oscillates around the centre of mass. The trajectory doesn’t corkscrew.
 
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Maple57 said:
I can remember one day at the range when we had to delay shooting because of fog. That was the only perfect day I can remember to test long range loads... just as the fog cleared and before the sun and wind kicked up.

It was absolutely dead calm and group sizes were crazy small for all of us on the base. We referred to that morning as a trigger pulling contest as scores were perfect across the board.

Unless you are testing long range loads under such conditions all you can really do is gusetimate the group within the group, but that is difficult to do.

If you ever get the chance to shoot as the fog clears and compare such a group to what happens the rest of the time, you'll see how much noise there is at medium to long range.

You can do a would have should have check on a shot to shot basis... or a post mortem... This is where you write down the scope setting... point of aim... and point of impact for every shot... then compare to condition changes to see if it was a wind read error or incorrect dope... or if you called it perfect... From that you can extract an idea of true accuracy... but you need to be pretty focused to figure it out. This is essentially how I've been plotting F Class scores for the past 20 years.

For those who dont trust your chronograph...

Accurate to 1/2 FPS... Got to get me one of these one day and test it.

Click to expand...

Now we are getting somewhere.... accuracy/precision doesn't happen by luck or hope.

Jerry
 
I think I recall reading that “the math” on the “cyclonic effect” works out to about .05” at 300yds.
 
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