Do you need at least 10 shots to establish a valid group?

R

rjinga

New member
I think my actual Google search term was "What's the significance of the three-shot group?" Within the first few search results was this post: http://www.bealeinnovations.com/stats-3shotgroup.pdf

Now, I admit that I'm not a statistician/mathematician/engineer; however, other than kind of losing me with his three dimensional graphs, everything else he wrote about actual shot distribution seemed to make sense. And, I agree with his grandpa - hitting what you're shooting at is the point.

So, with that in mind, I ran my most recent 10-shot targets back through the OnTarget app to display the mean radius circle (drawn using the average distance of all the shots from the center of the group) and the group extent box (created by drawing intersecting straight lines through the center of the most outlying shots).

The rifle is a PTR 91 GI Classic; the ammunition is MEN 16 7.62x51. Unless otherwise noted, all the targets were shot from a table rest with the iron sights.

xbtTHU8.jpg


vCB224c.jpg


UdHAbKD.jpg


When shooting this target I was sitting on a small block and resting the barrel on a rail.
DTBLo1Y.jpg


When shooting this target I was standing and using the sling.
P30QZnl.jpg


5KaONaF.jpg
 
Personally, I use 5 shots with a rifle, 10 shots with a pistol. Anyhow, have you tried shooting for group sizes using regular bullseye type targets rather than silhouette targets? You may find tighter groups.
 
I test my loads, when working them up, with four individual targets with five shot groups on them and one target that records all twenty shots as an aggregate. I do this several times over a couple of months to make sure I know what to expect from my loads. I am a hunter and I expect the first shot to kill cleanly and quickly. If it doesn't then I am responsible for the needless suffering of that animal that is giving its life to feed my family. It must be dead after the first shot.
 
I kinda got lost in all the math, but I've thought about this in the past and will use some math of my own in a minute.

Unless you NEED to fire more shots to compete in some sort of shooting game I think 3 shots are plenty to determine how accurate you load is and to verify zero. I think 5 shots is testing the accuracy potential of the rifle and more than 5 shots tells us more about the skill (actually concentration levels) of the person pulling the trigger.

Here is my math. If you fire 5 round groups each shot is 20% of the group. That means that any one of the 5 shots has a 20% chance of being the one the farthest from the rest of the group.

With that as a given shots 1-3 have a 60% chance of being the one that opens up the group the greatest, shots 4 and 5 have a 40% chance. If my math is correct then 60% of the time a 3 shot group should be no larger than a 5 shot group since one of the 1st 3 shots should statistically be the farthest from the group.

But in reality it almost never happens that way. We tend shoot very good 3 shot groups over and over and it is almost always either shot #4 or #5 that opens up the group when we shoot 5 shot groups. If we are testing the loads this shouldn't be happening.

As a hunter I believe a series of 3 shot groups tell me what I need to know. How well my rifle and I shoot for 5 or more shots is only relevant if I'm shooting in a competition that requires 5 or more shots. Hunting does not.
 
come on man, you are all over the new with this post. You have received very good advice on each and every forum.
Click to expand...
I have no idea what this guy said. Is that Orwellian "New Speak"? Can someone please explain it to me.
 
Quote:
come on man, you are all over the new with this post. You have received very good advice on each and every forum.
I have no idea what this guy said. Is that Orwellian "New Speak"? Can someone please explain it to me.
Click to expand...
Thinking it was mistyped, and supposed to be net. Probably seen the same thread on a bunch of forums.
Anyway, be it three, five, or ten shots, my thinking is that it is the consistency of the groups. A five shot, 3" group, followed by a five shot 8" group isn't a group. I guess in a way, the ten shots mentioned would be 3, 3 shot groups plus one, or two five shot groups. But I prefer the pause between groups to help prove consistency.
 
How many shots you need for a "valid" group depends on what you want the answer to tell you.

It came up in a discussion the other day, about groups sizes, and one fellow claimed a seemingly impossibly small group size with any, and all of his rifles.

He was shooting one shot "groups".

I can see the sense in averaging group sizes, to get a rough estimate of what your rifle, ammo, and you can be expected to do.

I don't understand what good averaging the shots inside the group gets you.
 
Just to make sure that there's no confusion when looking at my photos: the "W" and "H" are the width and height of the group extent box; the "Mean" number is the radius (distance from the center to the edge) of the circle, not a MOA.
 
Does a one shot "group" size equal the diameter of the bullet, one-half the diameter of the bullet, or zero.::rolleyes:
 
For me:

Typically 3 shots for a bolt-action, single-shot, and (probably) pump-action or lever-action. A cylinder-full for a revolver, because I want to check all the charge-hole/forcing cone combinations. Probably 5 shots for a semi.

The trouble with using larger numbers of shots, if your purpose is to get at the "intrinsic" accuracy of the firearm, is that it starts getting more and more likely that you will include some "random", non-recurring error that has nothing to do with the firearm (shooter error, unusual round, sudden gust of wind, etc.).

If you're using a Ransom Rest for handguns (and using it properly) at least that eliminates shooter error; I don't think there's an equivalent for rifles.

Now, if you're not testing the rifle, but the rifle/shooter combination, well, shoot as many as you believe you normally would at a single target, from the shooting position that you would normally be shooting, at the speed you would expect to shoot them.
 
Valid for what?

If I know the load and rifle well enough I might just fire one shot to verify zero after travel before a hunt.

There are some that will fire 30 round groups.

Most of the time I fall somewhere in between.
 
A guy over at ar15.com named Molon does a lot of accuracy testing of barrels/ammo and generally records 3 10-shot groups for statistical significance. Helps to even out outliers in data and give a better representation of actual accuracy over time. However he meticulously records conditions and rifle parts/ammo used when doing this testing. For the common hunter I suppose it doesn't matter really, for someone trying to eke out every last bit of accuracy I would think it's a different story. Allowing barrel to cool and loading single shots is also used in his testing.
 
Thinking it was mistyped, and supposed to be net.
Click to expand...


Yep, you are correct, I was trying to type [net]. I am not sure what answer he is looking for but this post seems to have appeared on just about every board that I frequent. Good luck
 
Last edited:
Since the "target" is a representation of an "enemy" soldier, we can assume "the enemy" will be firing back. So what will an "X" shot group prove, no matter what number X is? Either you "kill" him with your first shot or you won't get a second.

Jim
 
You must log in or register to reply here.
Back
Top