Accuracy and Precision

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AZSteve

AZSteve

Member
May 11, 2015
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Arizona, United States
I am looking for input from The Nation about these important aspects of our sport. I was talking to a co-worker and he mentioned how accurate his rifle is. His statement tripped a switch in my brain and I began to think about the difference between accuracy and precision. It seems that people use these terms interchangeably, but the more I thought about it, the difference between the two came into focus. When I was in the Army, we made a joke about how the Army operates. The joke was “measure it with a micrometer, mark it with a crayon, and cut it with an axe”. A micrometer is a precision measuring device. It will measure precisely what the user wants. However, it is only an accurate measurement if the user measures in the proper place. The crayon can accurately mark the measured location, but it is not a precise mark. Finally, the person using the axe may accurately place the axe’s cutting edge on the mark, but it will be an imprecise cut.The thought I have involves what is more important to each of these in our sport. My conclusion is that the equipment is more important for precision and the shooter is important for more accuracy. However, accuracy and precision go hand-in-hand in order to produce the results a shooter strives for. If you place a PCP in a rest and secure it without sighting in on the target, the size of the group is dependent on how precise the rifle is. When the shooter sights in on the target, the shot placement depends on how accurately the shooter sights it on the target. An accurate shooter with an imprecise gun will produce a large shot group as will a precise gun with an inaccurate shooter. Of course, the optic plays an important role in this, so this comparison is being made under the pretense that the rifle has a quality scope. I am taking the shooter’s precision (same trigger pull, sight picture, breathing, cheek-to-stock weld, etc.) into account based upon how it pertains to his/her accuracy. Therefore, I concluded that the correct way to describe the rifle is in terms of precision (my rifle is so precise that it produces one ragged 5-shot hole at 25 yards) and describe the shooter in terms of accuracy (I am so accurate that I shoot a ragged 5-shot hole at 25 yards). This is the short version of the debate I had with myself. I would like to hear input from The Nation in order to add more information to the topic based on other points of view to produce a more well-rounded conclusion. Thank you for your attention and input. Happy Thanksgiving to those celebrating today.
 
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Sounds like you have given this a lot of thought, I would like to add this. 25yards is in my humble opinion too close to judge accuracy and or precision, it is a good starting point but 50 yards is a better distance for most shooters. It give the pellet more time in flight too do travel how the barrel released it. Too many stories of great groups at 10, ok groups at 25 and horrible groups at 50 (yards that is). 1 inch groups at 100 yards is a good group by all our standards.
 
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Sorry about my lack of clarity there. The post is not about judging accuracy and precision, rather the difference between the two. The distance was just an example to plug into the sentence to illustrate the difference when talking about precision or accuracy. Any distance can be put into the sentence to illustrate the difference I am talking about. 
 
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I was once told (for what it is worth), that the difference between a good shooter and a poor one, was the multiplication factor between the ultimate precision (gun in a machine rest) grouping, and the shooter's off-hand grouping. In other words, assuming the weapon in question can shoot 1/2 groups at 100 yards; if the shooter can shoot good enough the keep the groups under 1 inch, he scores less than a 2. If his groups are say 2 inches, then he scores a 4. Like golf, the lower the score the better. 

Based on my 60+ year shooting career (I grew up in a sporting goods store), precious few folks score under two, and it is almost as rare to score less than three 3. I suspect most of us are closer to a 4, but only if we practice regularly. 
 
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From my chemistry days in college my professor made a point for us to differentiate these two terms. Most of us use the word accuracy to describe precision. We describe accuracy as hitting the bullseye. The "working" definition of accuracy is the ability to reproduce the results. Precision refers to the exactness of the measurement, meaning to the nth power. The number 1.00000 is more precise that 1.0. In actuality, the less precise we are the more accurate we become. Example: a larger target is easier to repetitively hit than a smaller one . Accuracy, again refers to the ability to reproduce the same result. Precision refers to the exactness of the measurement (closest to the bullseye).
I realize that I and most people will still use the word accuracy when they really mean precision. That tackdriver that hits the bullseye everytime is both precise and accurate, meaning it is able to hit the bullseye (precision) and repetively (accuracy). Precision may negatively influence accuracy as we attempt to narrow our target. 
Another way to look at this is when you are shooting groups. You don't care if you hit the bulleye. You are checking to see if the pellet hits the same spot and you would call this accuracy. When you are attempting to hit the bullseye you are shooting for precision. So really when you are saying you have an accurate shooting rifle, you really mean it shoots repetitively in the same spot. Precision is your ability to shoot an accurate rifle into the bullseye. 
 
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My wife debates with herself and somehow manages to lose most of the time. So is she accurate or precise?
Let's say I pour my 10 shot PCP gunstock in concrete and weld the barrel to a heavy metal workbench so that it absolutely cannot move. I am in the sweet spot for consistent FPS. I rip off 10 shots inside a building where there is no air movement. POA has remained constant. Chances are that the last 9 shots will not go into the exact same hole as made by the first shot. Why? Wouldn't it have to be that the pellets themselves are not "precise" enough to be completely "accurate"? 

BTW, NMshooter. How is 1.0000 more precise than 1.0? Which one is larger and by how much? Just askin'
 
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When I was testing barrels for my Falcon that was almost exactly what we did, we locked it in a vise. We tested the barrel to see which pellet had the tightest pattern. If the barrel could not shoot any pellet we went on to the next barrel. We did find a barrel that shot the Premiers well but the JSB's 14,35 were almost pellet on pellet (at 25 yds). We found that some pellets shot well close but not far. This is accuracy not precision. We were trying to see if the barrel was consistent with a particular pellet. this is what makes this hobby interesting. there are sooo many factors. If your goal was to place one pellet on top of one another you now have picked a target and now you are dealing with precision. There is a difference in these two terms and hopefully I will be able to demonstate by answering your next question:
The difference between the two numbers, 1.000 and 1.0 is the first number is measured to the thousandth place, it is more precise. An example are the JSB pellets 5.51, 5.52, 5.53. that .03 could make a big difference for some barrels (that 3 thousandth of a millimeter). If you had a caliper that only measured to the tenth place you would not be able to determine the difference. the caliper was not precise enough. 

So to recap thees terms as they apply to science:
 Precision is related to a unit of measurement. You have set parameters or a location. The more numbers after the decimal the more precise the number.
 Accuracy is related to the ability to get the same results (no measurement is needed). 
As it applies to shooting IMO: 
Accuracy would be how well your rifle is aligned to the pellet- tight group means more accurate, wide groups mean the barrel is less accurate
Precision how close you, the rifle, and ammunition can hit the bullseye. Has nothing to do with how many times you do this ( that is accuracy)! You have now picked a parameter to hit a given point. In benchrest they can measure how precise you can shoot by scoring. The score has nothing to do accuracy it is a measurement of their ability to shoot. 

I have attempted to apply these words from science to shooting. I know that these two words are easily confused and many people fail chemistry because they could not grasp these concepts. If I have failed to convey these concepts, I truly am sorry, I was not trying to be a wise-ass. What we really want is to do both, repeatedly hit the bullseye which is being both precise and accurate. Understanding these two terms is really important when you are not precise or accurate. Where do you start to fix the problem. this is what has brought me to this hobby. There is so much that can effect your shooting. this is how you would use these points:

Getting your gun to shoot accurate could involve shooting speed, pellet weight and size, barrel selection, hammer spring tension, transferport size, etc. 

Getting your rifle to shoot precise (hit the bullseye) would involve distance judgement, wind involvement, rifle being level, rifle being held by you properly, good scope and looking through it properly, shooter skill, etc.

Maybe if Harry chimes in on this he could be a much better teacher and I know could expound on the subjects. He is amazing


 
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I like this debate, it is something I have spent more than a few minutes on, trying to understand what people mean when they use those words.

Just to add in something, rightly or wrongly, I think of a guns ability as 'consistency'. If the gun is consistent and I accurately aim it, the result should be a pellet precisely placed where I intended... never seems to happens though!
 
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NM you bring up a question I have always wondered about when you mentioned the word "consistent". I can understand virtually every barrel being slightly different. What I don't understand is what changes in a barrel from shot to shot to make POI different. The only variable being a very slight difference in each pellet in relation to each other.
 
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another variable is the pellet speed. When you chrony your rilfe you will see how different the pellet speed will be. If you have an extreme spread of ten (say 890-880fps) you will have a very accurate rifle. Provided that pellet likes that speed. Large spread (890-780)- not accurate. when I was testing my Marauder the first 4 shots over several strings were the same and then it went to hell. Guess what- the first four shots hit the same place and then the placement was poor as the pellet speed dropped at avariable rates. Getting your rifle to get a small spread can be a feat in itself. getting the pellet to be the exact size and weight is also a challenge. 

So here is my wise-ass answer to accuracy and precise (just trying to be funny- not sure it will work)
When you say my gun can shot the ass off an gnat you are refering to precision. My gun can hit a gnat's ass
How many times you can hit a gnat's ass is talking about accuracy.
Precision always refers to a measurement
Accuracy is how many times you can do it.

Interesting point: JSB on the bottom has a measurement of 5.52 on their 18.1 gr pellet. If you were to measure all the pellet skirts you would find pellet size varies from 5.51 to 5.54. To improve their accuracy they only measure to the tenth power meaning 5.5. all the pellets are 5.5. To improve their accuracy they are being less precise. Precision is about measurement. Accuracy is the ability to reproduce. So to the question is 1.0 the same as 1.00000. the answer is I don't know, we didn't measure out that far. 1.0 could be 1.0 760. The bottom line to consumers is we want JSB to be both accurate and precise. We want all (accuracy) the pellets to be 5.52 or 5.53 (precision).
I know it is splitting hairs but these two terms are in fact very different.
Hope this helps
Doc
 
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If we limit our discussion to just the barrels, and whether one specific pellet shoots well thought it, when other don't; by necessity we need to look deeper than just say the twist rate. 

I don't remember the author, but there is a book about this very subject, albeit covering firearms. It not only mentions twist rates, it also considers consistency in barrel diameter as well as the ultimate diameter (ID vs. projectile OD), straightness of the bore (think cork screw), crowning, and even the throat design and length. I suspect very few in this hobby have the requisite equipment to measure any more than one or two of the aforementioned variables. This leaves us with the only one methodology, as mentioned above with respect to trying various barrels in a round-robin fashion. 
 
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You are correct that accuracy and consistancy are the same. Precision only is the measurement, parameters, or outcome that you set. As AZ shows with his diagram, we have set as our parameter that the bullseye is the most precise point, Accuracy is the ability to hit that point repetitively.

Don't want to confuse the issue but........... the less precise (the larger the target) the easier it is to hit so...... accuracy would improve. Accuracy does not always mean precision. 
 
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I thought of posting about this very same subject a few weeks back. I think we all get hung up on what accuracy really is. The oft-maligned Benjamin Rogue was an accurate rifle. Now before you laugh me off of the forum, let me try to explain. That gun might not have been set up to shoot the much sought after dime-sized groups at 100 yards. But taking that rifle on it's own merit, it was accurate within "it's" own parameters. We often find ourselves comparing one gun to another. And when we don't get the results we wish for, we simply call that gun inaccurate.

All guns are accurate. But some are better at achieving the results we want a bit better than others. I hardly ever hear anyone compare a Cricket, Wildcat, Royale, etc. to a match grade Olympic caliber rifle. Entirely different animals. but they are all accurate in their own way.

The only person I have seen to repeatedly create the same "laboratory" style demonstration on precision is the gentleman known as "Dirt E Harry", the owner of TopAirgun. Go take a look and this may lend some fodder for further discussion.

Keith.

(I only named the above rifles as examples. I am not picking on any particular brand!)

 
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