Measuring accuracy, I’ve been doing it wrong.

[BBerguson]

While searching the web you come across all kinds of things, in this instance, a better way to measure accuracy... http://www.ctmuzzleloaders.com/ctml_experiments/accuracy/accuracy.html

This is about muzzle loaders so maybe my opinion is too quick and too harsh but it is my opinion... And my opinion is that this is complete BS! I was a computer programmer for many years so this program “shoot groups” is based just on the random parameters (test group size) programmed into it. How about some variables that exist every time the MZ is loaded? Like: Temperature, wind, shooter ability, projectile quality, power quality, patch, patch lube, projectile seating consistency... Is all of this programmed into the computer or is it just a maximum group size programmed in so that is the largest your computer group can ever be? Along with: your bench, what you‘re wearing, how you feel, same lot of powder as your test group and on and on...

Wow, this is starting to sound like a rant... I guess it is. I’ve said for years that I don’t trust electronic voting because as a programmer (I was a database programmer and worked with data) I know how easy it is to change large amounts of data with a single command, in milliseconds... So, this being inauguration day, I’m ranting about things that in my opinion, are BS.

Back to the original subject. I honestly don’t see the value in creating groups with a computer program. Maybe the author learned a new programming technique or some new commands he wasn’t sure how to use but as far as determining the accuracy of a gun, I think not.

Ok, rant over...

 

[Ian]

I just use the scale on my Swiss Army knife to measure groups. I had as much association with statistical calculations as I will ever want in my lifetime when in college.

My best friend is a programmer. He uses a flip phone, drives 20-year-old vehicles, and hand deposits his paper paychecks.

 

[popper]

IIRC others call it the cone of accuracy or sumpin. Just a 'bell' curve for a statistically acceptable number of shots - from a reliable shooting base. Facy name for a typical bulls eye ring target. When I was doing guidance systems, called miss distance. Redefined when a laser guided air dropped missile hit the laser spot on the front tire of the jeep. Very slo-mo video.

 

[Jäger]

Well, Twain was wrong with "There are lies, damned lies, and statistics..." If he had substituted "Soviet Democrats" for "statistics", he would have been more accurate. Another saying about statistics is "Figures don't lie - but liars figure" - which is the cherrypicking of statistics and intentionally misleading statistics we're regularly subjected to these days.

One of our texts from the mandatory stats courses way back when was "How To Lie With Statistics" or something like that - I think it is still available for purchase. The actual intent is to teach how various errors can result in misleading results, not to teach how to deceive.

I didn't look at the article closely, but I did notice that CEP is being used as the standard for statistical analysis - the same standard as your Garmin GPS uses for telling you where you are. In the world of geomatics and doing surveys with RTK equipment, if I provided a client with location data and told them the standard was CEP - they'd throw me out on my ear. Garmin uses it because telling recreational users that the position their Garmin is giving them is accurate to within 5' (or whatever), makes them much happier than telling them it is accurate to within 20'. Professional GPS units allow you to specify positional accuracy through HDOP and PDOP (dilutions of precision) that throw out all the positional outliers and only use the data collected within a narrow window of the bell curve to ultimately give you your xyz coordinates.

CEP is essentially 50/50 as far as accuracy is concerned; in comparison the baseline norm for positional coordinates/data is two sigma, and increasingly, the industry is expecting three sigma. A small sliver out of the top of a bell curve, versus a slice of cake that goes 25% either way on the bell curve from a center line. Do you want your survey points (or your group on the target) to fall within a little sliver of the bell curve - or within roughly half of the total extent of the bell curve?

That's a poor word description, but I hope it suffices. I doubt there's a benchrest competitor out there who would be happy if the grouping ability of his benchrest rifle was repeatable only to CEP standards, versus three sigma. CEP accepts a LOT of fliers to give you a group size; three sigma goes a long way towards rejecting them.

There are other ways of illustrating the proper use of statistical analysis - proper being the operative word. For example, if I tell you I get half inch groups out of my Model 94 at 100 yards, how excited should I be if I also tell you that's for a three shot group I fired one time? How about if instead it was a 10 shot group fired several times in a row?

Proper statistical analysis of anything, whether the grouping ability of a rifle or of a particular load, or of the geographical location of a primary survey monument, requires context and a useful base of probability.

CEP does not provide that (at least in my opinion). Same reason I don't think three shot groups have much meaning unless you can get the same group size with five, ten, fifteen, etc groups fired in succession.

 

[fiver]

there's squares on the target.
those are about 1" across and about another from bottom to top.
if all the bullets are inside one of them and not touching the lines it's under an inch.
if some are touching the lines one way or the other it's an inch.
if they take up part of say 3 or maybe 4 squares they are probably closer to 2" groups.
if necessary I will grab the ruler and measure form one holes edge to another ones edge, I don't care all that much but 1-3/4 sounds better than 2.

 

[RBHarter]

I shot 250-300 rounds one summer .... Maybe more ....
In any case on a whim I took the stack of targets and plotted every hole about it's group center and on a center point reference .
The targets represented from zero to plus .5 gr and OAL adjustments . Turns out that well worn hunter grade rifle that has or had then a 5 shot .750 load and in the 30 or so yr it's been around me never shot less than 4" with I guess 15 different factory loads . The lot of 150 LC 43 was the exception and it scattered a dozen or so of them and shot 4 very round 2.7" groups about 18" apart at POH ,10:30 , 7:00 , and 4:00 . The conclusion at the end was that rifle was a solid 1.25 rifle and driver with entry level match like attention to load details .
If that one had been held to cone of fire .......well 3 feet @100 ain't much in the way of a hunting rifle ........its a marginal SD pistol .....

The old custom Carcano has never shot more than 3" 2 inches from POH at 100 from light cast to blown primer pockets . Which outside at something like 200 rounds total is 8" net . Good times there .

 

[Bret4207]

I've done more group shooting with 22's (back when they were available and cheap) than anything else. When I was wringing out my 52 Winchester and re-teaching myself how to use an externally adjusted scope, I was shooting 10 shot groups, often 30-50 of them. IMO, doing something like that over a day or 2 or a week or so tells you a lot more than the common 25 yds 3 shot group from the glossy magazines. It also lets you see where the variables stack up, things like light and wind and shadow and that dope behind the trigger! Using a computer might make sense if you can measure every group consistently, but I think laying out 10 10 shot targets give you a darn good idea of where the average looks to lay and that's probably the "group" that really counts.

 

[JonB]

In rifle league, we had a special tool for measuring groups.
Myself, I just eyeball it...that's probably why I ain't in the league no more, LOL

 

[BBerguson]

In rifle league, we had a special tool for measuring groups.
Myself, I just eyeball it...that's probably why I ain't in the league no more, LOL

Kind of like the old carpenters that would hold their thump up to plumb a wall!!! Lol

 

[BBerguson]

Of course the best way is to take your first shot and then sling the rest into the backstop, one hole groups every time! lol

 

[CZ93X62]

My shooting skills have degraded so badly over a couple years of disuse, I think a yardstick might answer as a group-measuring device lately.

 

[462]

Of course the best way is to take your first shot and then sling the rest into the backstop, one hole groups every time! lol

Many years ago, my now deceased shooting pard and I were at the local range. His first shot from his S&W 1917 perfectly centered the X. He packed up the gun and ammo, and got out whatever the next gun was.

 

[Missionary]

And then there are those who measure groups from the center of the bullet holes and do not say so.
I was taught to measure outside to outside of the whole and I will stick to it. If we were shooting matchsticks and a center hole measurer just grazed a stick I garantee he would claim what his full diameter hole did..

 

[RBHarter]

That makes 1 holt from a 480 the same size group as 3 22s touching on 2 points .

 

[BBerguson]

And then there are those who measure groups from the center of the bullet holes and do not say so.
I was taught to measure outside to outside of the whole and I will stick to it. If we were shooting matchsticks and a center hole measurer just grazed a stick I garantee he would claim what his full diameter hole did..

group is measured to the outside and then subtract 1 bullet diameter I thought everyone does it that way.

 

[Ian]

I just lay the scale/rule/ measure across the middle of the farthest two holes and measure outside to inside.

 

[BBerguson]

I just lay the scale/rule/ measure across the middle of the farthest two holes and measure outside to inside.

I’m sorry, yes, either way gives the same results.

 

[Ian]

With bullet-sized pegs inserted into the most distant holes, outside measurement with calipers and the subtraction of one bullet diameter is how match targets are often scored.

 

[CZ93X62]

I derive and report groups as center-to-center distributions, measuring as above. I really like the 1-inch checkerboard-type targets, esp. with scoped rifles.

 

[twodot]

........ If we were shooting matchsticks and a center hole measurer just grazed a stick I garantee he would claim what his full diameter hole did..

I thought the idea was to light the match, not cut it in two.
..