The PAM Syndrome

[Walkalong]

i dunno, a rifle in a machine rest might shoot 1 MOA. if you're a deer hunter, and that's a gun you paid $250 for, that level of precision is likely to be described as fantastic. if you wanted to use it for a bullseye competition gun, that level of precision is likely to be described as teh suq. It's up to the shooter to make it accurate by zeroing it, and later by accounting for environmental variables (distance, wind, angle, temp, etc)

Let's think about accuracy like headspace. The proper headspace must be built in. It is purely mechanical. Same for accuracy, it must be built in. What degree of accuracy one needs is determined by the usage. After that, the shooter has to bring the accuracy potential out of the gun.

Precision/accuracy is built into the gun. Being able to precisely place shots is a combination of a very accurate rifle and a shooter that can wring it out of the gun.

Give an inexperienced shooter a rifle capable of 1/4 MOA or less and a great shooter a rifle capable of 1/2 MOA or worse, throw in some less than stellar conditions, and the experienced shooter will beat them every time.

Precision is having the firearm make all bullets cluster in the smallest group with a fixed point of aim.

Accuracy is having the firearm center all shot groups on the point of aim wherever it's at.

I tend to look at this exactly the opposite as Bart, as I stated, but it doesn't make me right, or Bart wrong, as it is purely subjective IMO.

 

[taliv]

wrt headspace, let's say i wanted 1 thou of headspace

precision is the 3 decimal places, accuracy is the value == 1

e.g. .005 is still precise. it's just not accurate (not the value i wanted)

 

[Bart B.]

Some firearms are easier to shoot well.

One National Champion (and record setter) had his choice of three arms to use from the US Army Marksmanship Unit. He chose the least accurate one (as tested in machine rest) as he could shoot better scores with it. Its trigger was the most repeatable in pull weight and sear-hammer disengagement at let-off.

 

[Walkalong]

I had a Benchrest rifle that I shot quite well, but wanted a different action. I traded for another rifle with that action. Others could shoot quite well, but I could/did not. I regretted getting rid of the one I shot well. I ended up selling the second rifle and buying a third rifle, which, fortunately, I did shoot well. Should have stuck with what worked in the first place. Would have been cheaper.

A bird in the hand........

 

[denton]

Precision is having the firearm make all bullets cluster in the smallest group with a fixed point of aim.

Accuracy is having the firearm center all shot groups on the point of aim wherever it's at.

These are the standard definitions.

You can use non-standard definitions if you like, or make up new terms. But that is cumbersome and confusing because if you want to communicate clearly, you have to state your definitions each time: I define 'frisky' as meaning the ability to place shots close to each other. Well, OK. I have a frisky rifle. A lot of readers won't understand what you mean. It's easier for everyone if we just use the standard definitions.

 

[Bart B.]

I wonder why SAAMI came up with a glossary?

http://www.saami.org/specifications_and_information/index.cfm

 

[txblackout]

And still useless. If a rifle is capable of shooting small groups, it's the fault of the shooter, poor marksmanship, that they are not on the target.

You either have a rifle and ammunition capable of the task or not. The shooter is capable of the task or not. There are few situations, all of them specialized competition, where a group off target is of any use at all.

Sorry to sound so combative about this, but there is no practical distinction between the "precision" and "accuracy" in this context. It is a function of marksmanship.

They are indeed different when used properly (this is actually a mathematical concept), but this is an improper use of the terms. Precision, mathematically, refers to how consistent a result is in the presence of bias. Shooting small groups is not a battle against bias, it is management of variables. Thus, the terms has been mis-applied. Useless in the context of shooting.

It isn't just mathematics it is science. Accuracy is how close to the true value an instrument or test can measure. Precision is how repeatable the results are.

An accurate thermometer would give a result closest to the actual temperature. A precise thermometer would give you the same result over and over again.

The closest match for guns would be an accurate gun shoots where you meant it to go. A precise gun shoots to the same place every time.

 

[Walkalong]

From SAMMI Glossary

ACCURACY
In firearms using single projectiles at a given distance, is the measure of the dispersion of the group of projectiles fired. The optimum would be one hole no larger in diameter than a single projectile.

Which is similar to what I posted earlier:

To me an accurate rifle can shoot little tiny groups over and over.

I don't see "precision" in there.

But I still say it is subjective.

 

[Reloadron]

This thread from September of last year covers most of what is being mentioned in this thread with the same favor of and objections to certain terms and definitions. The last version ran 5 pages, so we still have about three pages to go.

Ron

 

[murf]

we have a lot more members, so hold on to your hat!

murf

 

[denton]

ACCURACY
In firearms using single projectiles at a given distance, is the measure of the dispersion of the group of projectiles fired. The optimum would be one hole no larger in diameter than a single projectile.

It's not the only factual error that SAAMI has made.

There is a large body of well-respected work that uses the standard definitions. Wheeler's book on Measurement Systems Analysis is probably as good as you can find.

 

[Nom de Forum]

This thread is beginning to remind me of medieval debates about how many angels can dance on a pinhead.

 

[1911 guy]

Ten thousand. All who disagree shall be burned at the stake.

The standard definitions are indeed correct. I just think they are being misused in the wrong context. When a rifle is capable of repeatable performance (precision), whether sub MOA or 5 MOA, all else is reliant on the shooter. The ability to place a group on target (accuracy) is a function of marksmanship and therefore, in the context of shooting, not a separate issue as it would be in mathematics or metrology.

 

[Bart B.]

"Head space" is the term that probably has the widest spread of meanings relative to the chamber or case.

"Caliber" may well be in second place.

"Magazine" and "clip" are probably tied with "caliber."

"Throat," "leade" and "free bore" rank near the top, too.