#14 Be Scientific: Shoot More Bullets Per Group

[hereinaz]

Three shot groups are a common way to test the precision of a rifle, but they are not statistically valid. This is because three shots is too small of a sample size to draw any meaningful conclusions about the rifle's accuracy.

Think of factors that can affect the accuracy of a rifle system, including:

• The quality of the rifle itself
• The type of ammunition used
• The efficiency of the cartridge
• The consistency of the bullet construction
• The size of the scope crosshair
• The size of the aim point
• The magnification of the scope
• The parallax of the scope
• The temperature of the barrel
• The dirtiness of the barrel
• The variation in the trigger break
• The variation/slop in the bolt lockup
• And many, many more factors

Any one of these factors can cause a variation in the shot, even if the rifle system is perfectly aimed and trigger pressed flawlessly. When you only fire three shots, you are much more likely to get a good group due to random chance.

When you don't get a group, the tendency is to say, "I pulled that one" or "that's a flyer" and not count it. But, as you keep shooting you'll find that most shots probably group close to the small "when I do my part" group, but you'll have statistically valid distribution of "flyers" all around the center group.

Go read what Bryan Litz writes about scientifically testing precision of a rifle. Look at his WEZ software that actually completes the statistical analysis for shooting.

Now, some rifle disciplines create super small groups, but look at what factors they control that we typical hunters do not. You might want to compare yourself to them and say your 3 shot group is representative, but if you aren't doing what they are doing, you won't get what they got. Besides, Bryan Litz is a competitive shooter, so it isn't as if he doesn't already take that into consideration--besides being a rocket scientist or something.

To get a statistically valid measure of a rifle system's precision, you need to fire a much larger group of shots. A good rule of thumb is to fire at least 10 shots, but preferably more. This will give you minimal data to smooth out the effects of random chance and get a more accurate picture of the rifle's true precision.

After you test precision, move the center of the group to the center of your aim point.

How to validly test the precision of a rifle​

It is important to note that the rifle's precision is not the same as its accuracy. Accuracy is a measure of how close the rifle's point of impact is to the point of aim. Precision is a measure of how tight the rifle's group size is. A rifle can be very precise, but not very accurate. For example, if you have a rifle that is zeroed at 100 yards, but it shoots consistently 2 inches to the left of your point of aim, the rifle will be very precise, but not very accurate.

To validly test the precision and accuracy of a rifle, you should follow these steps:

1. Choose a target that is appropriate for the distance you are shooting at. A good rule of thumb is to use a target that is at least 12 inches wide by 18 inches tall.
2. Fire at least 10 shots at the target, but preferably more.
3. Measure the center-to-center distance between the furthest two shots. That is the precision of the rifle system.
4. Measure the distance from the center of the aim point to the center of the group. That is the accuracy of the rifle system.
5. Calculate the center of aim point to-center of furthest bullet distance. This is the rifle's actual accuracy and precision--not just group size.

You can also use a statistical calculator to calculate the rifle's standard deviation. This is a measure of how spread out the shots are. A lower standard deviation indicates a more precise rifle.

To improve the accuracy of your rifle, you need to sight it in so that the point of impact matches the point of aim. Once the rifle is sighted in, you can improve your precision by practicing your shooting technique and using higher-quality ammunition.

How to FURTHER test the precision of a rifle​

If you want to know how much YOU influence the rifle to make a group bigger, find someone who is a better shooter than you. Give them 10 rounds to fire from your rifle and shoot 10 rounds from their rifle. Then compare the groups. Assuming there isn't some influence like differences in trigger weight, rifle stock configuration, etc. you can get a good idea of your effect on the size of the groups.

On at least one occasion, I wanted to test this, so I swapped out my barreled action into a friends stock and had them shoot my barreled action and scope. We both had the same trigger, so that was apples to apples. Nearly every time we shot together, he always shot better with my rifle. So, for that experiment, I was able to get an idea of how much I was influencing my rifle.

It humbled me, cause I couldn't blame flyers on the rifle. I knew it was all me.

Now, when I go to the range, when someone complains about their rifle, scope, or ammo, I always ask if they would like me (or my friend who is a better shot) to give it a go, just to confirm that "this rifle and scope sucks" so they can go ahead and sell it. The last time I did that, it was a 300 RUM that was shooting 3 and 4 inch groups for my buddy. It is a Rem 700 varmint that is a pig of a rifle, meaning it ain't light.

That rifle still beat the living crap out of me, I hate recoil, hurts my neck and head. I limited that punishment to 4 shots, but at 1.5" the group was enough to convince my buddy that it was him not the gun. He still hasn't given up the idea that he is tough enough to shoot the RUM without flinching. But, I think after that range trip, he might consider my yearly suggestion to sell it and get a lighter recoiling rifle.

 

[JF_Idaho]

There's plenty of other threads recently that discuss this. But, to start a conversation......

One 10 shot group holds more statistical value than One 3 shot group. Obviously.

I will argue that Three 3 shot groups over 2 or 3 shooting sessions, gives more statistical value than One 10 shot group, in this case using 1 less round.

Either way, I generally shoot 5 round groups. Usually multiple, though. It's worked for me.

 

[hereinaz]

Yes, stacking multiple 3 shot groups is better because you introduce shooter variability into the situation.

I am doing explanations here so a shooter can have one place to look and find info without as much scrolling. I agree the discussions are really helpful.

 

[TaperPin]

That rifle still beat the living crap out of me, I hate recoil, hurts my neck and head. I limited that punishment to 4 shots, but at 1.5" the group was enough to convince my buddy that it was him not the gun.

All good points, and I’m not dismissing the value of whatever it takes to reach a conclusion - and the one thing I’d add is experience and familiarity.

Take a random dude who has never handled a gun, go through the basics so he’s safe and turn him loose at the rifle range and reloading bench. He will struggle through every aspect of shooting. Will the first 1000 shots tell him much about the rifle or loads? I say no. Even 10 shot groups still only shows the outline of an onion with 100 layers - knowledge and skills pull away layers of the onion and group size shrinks. Everything from how to clean a barrel, how to squeeze a trigger, to the most advanced issues of reloading and rifle barrels - including every physical aspect of the gun.

Now take an old geezer who has worked through much of what’s considered important, picks up an unknown rifle, and in only 4 shots there is a lot of useful new information about the rifle.

Likewise, different combinations are known to shoot within accuracy ranges - as more layers of the onion are optimized the tighter those accuracy ranges become. If an experienced shooter with a brand new bottom of the line mil spec ar15 and ball ammo shoots a 1 moa 3 shot group that’s most likely not a moa gun and groups would be expected to open up with more shots. On the other hand if a national champion benchrest shooter with his favorite action and barrel, chambered by his favorite gunsmith, shoots the first two shots of load development 1/8 moa apart from a brand new rifle, we would expect the ultimate accuracy of his setup after load development to be better than that.

If nothing else large round counts encourage practice, which everyone needs.

 

[hereinaz]

@TaperPin I agree, that the more data a guy has, including prior experience, the more value comes from a three shot group. I think that is why I will shoot a three shot group on a proven rifle to check my zero, and feel good about it without shooting more. I am mentally laying those three shots over the top of all the prior shots.

I bet that is what others are doing as well.

I think it is self deceptive when someone shoots a tiny group, and then says, "that is what the gun is capable of, when I do my part." You gotta take into account all the shots before. If they are all small groups, before, then yeah, its duplicating what it did before.

That goes right along with what you said.