Measuring Accuracy As Opposed To Precision

JumboJVT said:

You can look at it any way you want, but either MOA or inches, its about the diameter of the of the circle described by the shots, not the radius.

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MOA is a unit of measurement to describe the angle of the cone which projects the circle onto the target. That circle can be measured in inches, but not actually measured in MOA. Defining MOA dispersion REQUIRES a relative distance, else it cannot be defined.

Equally, inches of group size, whether diameter or radius, are largely meaningless without a relative distance - a 1/2” group might seem great, but if it is fired with a $5,000 rifle at 25 yards, it’s crap. A 10” group might seem poor, but if it was fired at 1400 yards, it’s great.

Frankly, radius of the group does matter. First, we cannot have radius without diameter, and cannot have diameter without radius. Radius reflects the dispersion of the shots from their centroid - and we typically try to place the centroid of our group onto the center of our target - aligning POI to POA. In MOST applications, we need to understand how far from our POA that bullet will strike. In hunting, I don’t care about diameter at all - I want to know that if I aim at the center of where I believe the heart to be, my bullet will still land within the edge of the projection of the heart. In PRS competition, I need to know that if I aim on target, my bullet will land within the edge of the target. In Service Rifle competition or Benchrest or F-class, I need to know my shot will land within the edge of the scoring ring. In EVERY case, the radius from where I will center my “cone of dispersion” on the target - where I place my POA - to ensure the RADIUS of the cone does not slip off of the edge of my target, whether that’s a heart, a steel plate, or a scoring ring.

Only in Internet discussion of group size does group diameter really come into play.

Atavar said:

Precision is inherent in the firearm/ammo.

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Not entirely apt, despite the lies we tell ourselves as shooters.

The firing system always involves something which supports it and fires it. When I shoot a rifle, the resulting groups on target will be more precise than when my 8 year old son shoots it. When I shoot my rifle, standing while supported on a barricade, the resulting groups will be less precise than when I fire prone from a bipod and bag. Even when I shoot prone from the bipod and bag and I’m dropping shots into one hole, I’m part of the equation - as my son won’t deliver groups as precise as I, even prone. On days when I have not slept well or don’t feel my best, my groups open up. Even locking the rifle into a vise and firing remotely, the resulting remains dependent upon the stability of the mechanism firing it. So we tell ourselves that Precision is only about the rifle and load - because in theory, the rifle will disperse shots within the same statistical deviation regardless of the shooter, but it really isn’t. We can’t actually measure that raw potential Precision, so it becomes irrelevant.

Equally, we know we can influence velocity and POI simply in how we support and fire the rifle - so it’s not fully true to claim even the raw precision of a rifle and load is completely independent of the shooter behind it.

someguy2800 said:

I would disagree with that if you also have accurate chronograph data.

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Chronograph doesn't mean a thing except how fast and how similar the rounds are traveling . nothing to do with accuracy or precision.
6 mm PPC is probably the one exception to 100 yard accuracy. ( my grandmother could shoot small groups with a 6 ppc) IMHO anyway

I would think if you had actual and accurate chrono data on the rounds you were shooting, you would have a better chance at better precision at distance.

Sort of like knowing what the distance and angle are, that gives you the offset in MOA would be along the line. Trajectory needs accurate data to give you more accurate results.

Of course, in some respects, thats all part of making yourself crazy too, if you want to jump into that rabbit hole.

trackskippy said:

I would think if you had actual and accurate chrono data on the rounds you were shooting, you would have a better chance at better precision at distance.

Sort of like knowing what the distance and angle are, that gives you the offset in MOA would be along the line. Trajectory needs accurate data to give you more accurate results.

Of course, in some respects, thats all part of making yourself crazy too, if you want to jump into that rabbit hole.

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Chronograph information is definitely handy when calculating a firing solution.

South Prairie Jim said:

Chronograph doesn't mean a thing except how fast and how similar the rounds are traveling . nothing to do with accuracy or precision.
6 mm PPC is probably the one exception to 100 yard accuracy. ( my grandmother could shoot small groups with a 6 ppc) IMHO anyway

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If your precise at 100, and you have good standard deviation of velocity, and the ballistic coefficient is known, then you know what is going to happen at longer ranges. Bullets don’t change their mind and decide to become inaccurate after passing 100 yards. If what is predicted doesn’t happen, then you have bad data.

As a longe range 1000 yard competitor, I can say with personal experience that small groups with excellent chronograph numbers at 100 yards wont automatically translate to small groups at 1000.

I wish it did but it does not... I will add that good consistent long range groups will almost always have good numbers .

There is no substitute for actual shooting and confirming, and of course, there is more to it than just the trajectory.

Having the right information available to you, can still make things a bit easier, and help you make better decisions and choices.

South Prairie Jim said:

As a longe range 1000 yard competitor, I can say with personal experience that small groups with excellent chronograph numbers at 100 yards wont automatically translate to small groups at 1000.

I wish it did but it does not...

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Agreed. Short range groups and stable velocity don’t always hold together at distance.

However, we also know a small shooting load at 100yrds which DOES NOT have consistent velocity invariably won’t shoot small at 1,000. So if a load shoots small AND has consistent velocity among shots, you have a chance. If it only shoots small, but varies greatly in velocity, you don’t.

I keep this picture around to remind myself of that fact. The target on our left has 3 shots low, after which I dialed to raise the waterline, then 12 more. Both targets at 875yrds. Both of these loads shoot small at 100, but the one on our left had only 24fps ES, the group on our right has 78fps ES.



In the context of the thread, accuracy of both loads is relatively similar - the group on the left hand target is centered a little right of POA, the group in the right hand target is centered a little below POA (I do forget now the wind call). But obviously the precision of the right hand group lags that of the left, even though at 100, the difference between precision of each was virtually null.

Accuracy is a function of the rifle, ammo, and to a lesser degree the skill of the shooter. A lot of inexperienced shooters can shoot small groups with a good rifle and ammo when firing from a supported position.

I work on accuracy 1st and don't worry about where the bullets are impacting. In fact it is easier to shoot small groups if the bullets impact somewhere other than the aiming point. Once you destroy the aiming point with bullet holes in the target you no longer have the same aiming point.

Once I get the accuracy I want I can always adjust the sights to hit where I'm aiming. After that the shooters skill starts to have more of an impact on precision. You have to judge wind, and calculate for bullet drop, (or rise), to get the bullet to impact at the point you want to hit. And you don't necessarily want to hit POA. Depending on the range and conditions you could be aiming above, below, to the side, or a combination of those to hit the desired target.

"It’s not so difficult: group size is precision. Group position is accuracy." Yep in spades, Rod

"I work on accuracy 1st and don't worry about where the bullets are impacting. In fact it is easier to shoot small groups if the bullets impact somewhere other than the aiming point. Once you destroy the aiming point with bullet holes in the target you no longer have the same aiming point." Also true in spades....Rod

I Hate to be repetitive, but see
http://www.columbia.edu/~to166/hiawatha.html

I am interested in practical hunting accuracy. I shoot a three shot group, then estimate the center of mass of the the triangle formed by the holes, I then adjust the scope so that this central point is as close to the point of aim as possible given the limitations imposed by the scope adjustments, which are usually 1/4" to 1/2" at 100 yards (I am still sorting out the MIL system--I only have one scope that uses it an it is in reserve for my 30-30 Contender project). I shoot another 3 shot group to verify, call it done, and go hunting...

Things would be different if I was seriously punching paper or shooting at more than 250 yards.

Atavar said:

A better scope does not make a rifle more accurate (unless the first one is broken). It just makes target acquisition easier.

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Not entirely accurate.... I find it much easier to shoot better when I can see better.
The scope on my brother's Parker Hale in .270 is an old Bushnell 3-9x40. The quality of the optics was never top drawer and after 50 years of hunting, the image quality is even less. My Tikka T3 Lite in .270 has a Vortex 6.5-20x50 Viper. Shooting the Tikka precisely to the desired point of aim is much easier than it is with the old Parker Hale.
Take note: That old Parker Hale is every bit a good shooter as my Tikka. I know it is because I worked up handloads for both rifles.

Poper said:

Not entirely accurate.... I find it much easier to shoot better when I can see better.
The scope on my brother's Parker Hale in .270 is an old Bushnell 3-9x40. The quality of the optics was never top drawer and after 50 years of hunting, the image quality is even less. My Tikka T3 Lite in .270 has a Vortex 6.5-20x50 Viper. Shooting the Tikka precisely to the desired point of aim is much easier than it is with the old Parker Hale.
Take note: That old Parker Hale is every bit a good shooter as my Tikka. I know it is because I worked up handloads for both rifles.

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Because the target acquisition is easier. It doesn’t make the firearm more accurate.
Easier is not more accurate.

Atavar said:

Because the target acquisition is easier. It doesn’t make the firearm more accurate.
Easier is not more accurate.

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Better optics certainly can and do make a rifle more accurate - again, reminding that the definition of accuracy is how closely the shot lands relative to the point of aim. As I described in my last response to you above, we cannot truly ignore the shooter within the firing system - ESPECIALLY when it comes to accuracy (the former response, in contrast, being focused on shooter influence upon precision).

We can’t hit what we can’t see. So when using a “better optic,” presuming “better” defines that we can “better” see the target, we’re better able to 1) place the POA more accurately on the target, and 2) more repeatably place the POA such the resulting POI’s are also tighter, yielding improved precision. So you really cannot dismiss “target acquisition” as irrelevant.

We can’t continue lying to ourselves as shooters that we don’t influence both accuracy and precision. Even when we do as much as can be done to reduce shooter influence, there always remains some mechanism which supports the rifle, another which catches recoil of the rifle, and another which fires the rifle - all of which influence both accuracy and precision.

Reading all this gave me a headache. I like the bullet to go where I am aiming and put alot of work into it. Not really concerned if you call it accuracy or precision. I try to make the rifle shoot as accurately as I can, I adjust it so the poi is the same as poa. I use scopes so I can see better as well as make more precise adjustments. I use a benchrest to establish rifle accuracy. Once I know where the rifle shoots different positions, ranges and conditions need to be practiced. I call it all accuracy. It's too complicated to divide it between precision and accuracy for my old brain.

An example of something that is precise but not accurate to me is a lot of traditional walnut stocked hunting rifles with full forend contact or “pressure bedded” forends. They aren’t all like this of course, but I’ve seen many of them that shoot nice tight groups when the owner comes to do their annual sight in, but that group is often 3 inches right and high, or left and low, or whatever. Then the owner admires there nice group and makes their scope adjustment, shoots another, puts the scope caps back on till next year and leaves. Well if you have to make short range zero adjustments every time you sight in the gun then something is moving, ie the wood stock expanding and contracting with temp and humidity and pushing on the barrel. I always wonder with some of these if the temp is 40 degrees colder when they are actually hunting will the POI be back to where they started? How about when it’s soaking wet vs completely dry? To me an accurate rifle is one that I can depend on to hit where I’m aiming without having to make a zero adjustment.

I have a 444 marlin handi rifle that I’m really fond of. It strings vertically as the barrel heats up. If you shoot a 5 shot group the first shot will hit home, 2nd shot will be an inch above that, third shot will be 2 inches high, 4th and 5th will settle out at about 2.5 inches high. If you wait half an hour the first shot will be back in the center. If you want to shoot a nice small group you just adjust your point of aim for the stringing and you can basically stack them. So if you take that gun out of the safe it will hit where you aim every time first shot, and by that definition it is precise and accurate, but if you go by group size it is neither precise nor accurate.

For me accuracy and precision combined is all that matters with any significant first shot "cold clean" bore differences really important for hunters.

Hang a 2 MOA steel plate target if you are missing it with a "1 MOA gun/ammo" you are not accurate. Missing with the "cold clean bore" first shot is of particular worry, especially for hunters. To me this is the only definition of accuracy/precision that really matters, the rest is just bragging rights.

I usually shoot 2 MOA mil-surp ammo so a 4 MOA steel target works similarly for me. Hunters should use a target whose MOA equals the "vitals" the prey at the maximum range you will ever shoot.

Graphic training aid on the subject:

South Prairie Jim said:

One thing for sure..100 yards damn sure isn't far enough to determine accuracy or precision.

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I do it all the time

Let me put it this way. If it doesn’t shoot small at 100, it damn sure won’t shoot small at longer distances

Nature Boy said:

I do it all the time

Let me put it this way. If it doesn’t shoot small at 100, it damn sure won’t shoot small at longer distances

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Yeah' but your one of kind Bro.

South Prairie Jim said:

Yeah' but your one of kind Bro.

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Hey, I appreciate that. Tell my wife!

With the assumed definitions that precision is tiny groups and accuracy is the group is centered on the POA...

Precision is hard and Accuracy significantly easier to achieve. If the combination of shooter, rifle, and ammo produces high precision than accuracy is simply a matter of measuring and adjusting the sighting system. We can extend this thought to additional ranges if we have an accurate ballistic model of the bullet in question once we have acquired the needed data (muzzle velocity, Ballistic Coefficient etc).

A combination that does not produced high precision will never produce great repeatable one shot accuracy, even if the average group is perfectly aligned with the point of aim. It easy to have great accuracy with a high precision combination. If you do not have high precision combination to start with it is hard to have high accuracy, especially as the group sizes gets smaller, approaching one.

I have always measured both precision and accuracy with my rifles when evaluating. In practice both are important. There are a bunch of applications available now that does all the math for you. I like Range Buddy, snap a quick picture of the target and a little bit of manipulation in the program and you get all the data you would need in most cases.


A nice example. The results gives me the group size and the distance the mathematical center of the group is from my designated point of aim. Easy to evaluate both the precision and accuracy from this data and if I repeat it several times my confidence in my numbers is increased, assuming the results are consistent.