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P2000
06-02-11, 23:27
If this has been covered already, I apologize.

To my annoyance, I hear the term MOA being thrown around constantly. Not just online, but everywhere people talk about accuracy. The way most people use the term MOA is an absolutely meaningless measure of accuracy.



For example,

"My rifle/load shoots 1/2 MOA"
This statement might really mean that the extreme spread of the best 3 shot group measured 1/2'' at 100 yards. The next group could have easily measured triple the size, or 1.5''.


With the availability of free calculators online which will quickly measure 10 shot groups using the superior ATC(Average To Center), what do you think about trying to make it the "norm". It would make it easier for us to know someone's method of determining group size, adding value to their statement. For example:


"My rifle/load shoots 0.212 10SATC"
With this statement, we know we are talking about a 10 shot group measured with a calculator tool, using ATC. A subsequent group is unlikely to measure significantly different, perhaps 0.290. Definitely not triple, or double.

What do you think? Would this ever catch on? I realize many members already measure ATC, because M4carbine is ahead of the game, but If we started using 10SATC, it may catch on.

Cameron
06-03-11, 01:05
Relax mate, we know what people mean when they say 1/2 MOA.

Cameron

montrala
06-03-11, 17:49
You have something like that in mind?

http://img.photobucket.com/albums/v286/montrala/Range%20reports/RUAG100m3.jpg

100m, HK MR223, Ruag 55gr FMJ bulk ammo, Aimpoint CompM4S, rifle rested on backpack.

10 shots ATC has this good side, that lone "flyer" does not kill ability to compare groups so much, without need to remove "called flyer caused by some butterfly passing near bullet" from equation.

I use only 10 shots groups and ATC as main indicator if given change to rifle or ammo resulted in gain or loss for accuracy.

For hunt of best CTC groups nothing beats 1-shot groups :jester:

P2000
06-04-11, 02:16
You have something like that in mind?

Exactly. Real data with solid statistics. Nice shooting.

Also, you bring up a good point about flyers...with ATC they don't throw off your group too badly. With the other method, people tend to just shoot more 3 shot groups until they are pleased.

QuietShootr
06-04-11, 09:13
Where can i read more on this? I'm ashamed to say that i work with statistics a lot, and this idea never occurred to me. Really, it makes a hell of a lot of sense- since there are a lot of reasons that a flyer can happen, and they aren't all indicative of the system's capability. Accounting for outliers but not allowing them to define the distribution is brilliant.

sinister
06-04-11, 10:49
What you call "Average to Center" is the "Mean radius" -- how the Army measures match rifle and ammunition performance.

The AMU typically proofs match rifles, pistols, and carbines from machine rests, usually three ten-shot groups, measuring bullet speed at 10 feet from the muzzle and at 300 meters.

Molon has written and photographed wonderful ammunition proofing groups, both here and on the other site.

shootist~
06-04-11, 11:13
Molon's posts dealing with testing various ammo usually include the mean radius of the groups, which is the same thing as ATC. I've always considered (just by eyeballing) how a group "clusters", or fails to cluster most shots near the center. Crude, but similar.

On Target software is a better way to do this that just using the Mk1 eyeball.

http://i4.photobucket.com/albums/y141/shootist87122/AR15/TargMk262and77SMKRLs03-11.jpg

Tuukka
06-04-11, 12:21
Well, having an accurate semi auto makes this whole thing a bit easier:)

http://www.aseutra.fi/finnish/product/HK417_SL5-BL.JPG

P2000
06-04-11, 22:18
Where can i read more on this? I'm ashamed to say that i work with statistics a lot, and this idea never occurred to me. Really, it makes a hell of a lot of sense- since there are a lot of reasons that a flyer can happen, and they aren't all indicative of the system's capability. Accounting for outliers but not allowing them to define the distribution is brilliant.

I remember some posts by Molon, which actually got me using the online calculators awhile back. I would try and find those and read up if possible.

I will try and explain why fliers are less important with Average To Center than Extreme Spread.
-With ATC, every shot is a data point. In other words, a 10 shot group has 10 data points, which are the distance of the shot to the mathematical center of the grouping. One flier only has 1/10 of the weight of the group...it isn't going to matter that much. With 10 shot groups, you can shoot group after group and they are going to have relatively similar ATC values.
-With ES, only the distance between the two farthest apart shots are counted. This means that with a 10 shot group, there is only one measurement, or one data point. So you could have a dime sized 10 shot group with one flier, and your group measures very poorly.

I would download the free copy of the older version calculator at http://www.ontargetshooting.com/download1.html

Give it a try. All you need to do is take a picture of your target, preferably with a ruler on it. Then upload the picture into the calculator software, set the scale based on the ruler, enter the bullet holes and voila...reliable statistics at one's disposal.

QuietShootr
06-04-11, 22:39
I remember some posts by Molon, which actually got me using the online calculators awhile back. I would try and find those and read up if possible.

I will try and explain why fliers are less important with Average To Center than Extreme Spread.
-With ATC, every shot is a data point. In other words, a 10 shot group has 10 data points, which are the distance of the shot to the mathematical center of the grouping. One flier only has 1/10 of the weight of the group...it isn't going to matter that much. With 10 shot groups, you can shoot group after group and they are going to have relatively similar ATC values.
-With ES, only the distance between the two farthest apart shots are counted. This means that with a 10 shot group, there is only one measurement, or one data point. So you could have a dime sized 10 shot group with one flier, and your group measures very poorly.

I would download the free copy of the older version calculator at http://www.ontargetshooting.com/download1.html

Give it a try. All you need to do is take a picture of your target, preferably with a ruler on it. Then upload the picture into the calculator software, set the scale based on the ruler, enter the bullet holes and voila...reliable statistics at one's disposal.

I'm sold. I'm going to shoot my 300 early in the morning, and I'm going to process the data with the software and see what I come up with.

ColtJ
06-04-11, 23:59
Good points.

I tend to use an app on my cell phone but it measures based on the two farthest points. 'Target Calculator' on Android.

As far as the number of rounds, for discussions sake maybe we should set regulations such as minimum shots per group atleast within the forum, etc... IE: 3 round sub MOA and 10 round sub MOA groups are two different things and not comparable even though both are "sub MOA".

For reference heres a group using the software mentioned above:

http://www.dragonape.com/AR15/6.jpg

mizer67
06-07-11, 20:43
Good points.

I tend to use an app on my cell phone but it measures based on the two farthest points. 'Target Calculator' on Android.

As far as the number of rounds, for discussions sake maybe we should set regulations such as minimum shots per group atleast within the forum, etc... IE: 3 round sub MOA and 10 round sub MOA groups are two different things and not comparable even though both are "sub MOA".

For reference heres a group using the software mentioned above:

http://www.dragonape.com/AR15/6.jpg

There appears to be something wrong with that program or the data input into the program. MOA is calculated improperly, or so it appears.

ColtJ
06-08-11, 09:52
There appears to be something wrong with that program or the data input into the program. MOA is calculated improperly, or so it appears.

May I ask why you think it calculates improperly?

Thanks.

mizer67
06-08-11, 13:48
May I ask why you think it calculates improperly?

Thanks.

1 MOA = 1.047 inch @ 100 yards.

Your picture from the application you'd posted shows them as equal to each other, for example, 1.050 inches = 1.050 MOA. That is a minor flaw in the program or data, or so it appeared to me.

Travis B
06-08-11, 17:36
1 MOA = 1.047 inch @ 100 yards.

Your picture from the application you'd posted shows them as equal to each other, for example, 1.050 inches = 1.050 MOA. That is a minor flaw in the program or data, or so it appeared to me.

Yeah, I noticed that flaw as well. But who's splitting hairs?

ColtJ
06-08-11, 20:25
I see. Missed that completely.

Its still a convenient tool and guess i can do the math myself to get the exact result.

ROGOPGEAR
06-09-11, 20:22
There appears to be something wrong with that program or the data input into the program. MOA is calculated improperly, or so it appears.

technically yes. practically, it doesn't matter. most consider 1inch to be MOA at 100yds and just drop the .047 for ease of calculations. At 1000yds that difference doesn't even equate to 1/2 inch yet. but, for a technical program, you could consider that an oversight.

mizer67
06-09-11, 20:48
technically yes. practically, it doesn't matter. most consider 1inch to be MOA at 100yds and just drop the .047 for ease of calculations. At 1000yds that difference doesn't even equate to 1/2 inch yet. but, for a technical program, you could consider that an oversight.

Yes, I know.

I just can't stand a lack of attention to detail in my line of work. It's a compulsion.

P2000
06-09-11, 22:02
For a phone app, that is pretty neat. At least a 10 shot group is used, and you could correct it to actual MOA if you wanted to.

However, I will still beat the "ATC is better" drum.

Remember that with extreme spread, you are only measuring the difference between your two furthest apart shots.

If you shoot several 10 shot groups and calculate both extreme spread and ATC on each group, you will most likely observe that the extreme spread tends to vary more from group to group. ATC tends to be more consistent.

Using ATC, every shot is measured by how off center it is. But with ES, a shot being off center may or may not matter, depending on where the other worst shot has landed....it makes little sense. As a shooter, we are trying to hit a target, not make our misses closer to our other misses.

For an extreme example, imagine one group shaped like a doughnut, where no shot hits the center, but all shots miss around the perimeter. Then imagine another group where you have 8 dead center hits, but two shots that are off. Both of those groups could have the same ES measurement, but using ATC the group with 8 hits would measure significantly better. It should measure better because you hit dead center 8 friggin' times!

P2000
06-09-11, 22:37
Here is a quick and sloppy illustration of my last point. Please note that this is just an extreme example to highlight the differences between ATC and ES.

Using ES, these groups measure about the same. Using ATC, these groups are very different. Clearly, the first group is much better, and ATC shows it.

Group 1. ATC= 0.251 MOA
ES= 1.474 MOA

http://i82.photobucket.com/albums/j248/87228/TgtGfx.jpg


Group 2. ATC=0.700MOA
ES=1.519

http://i82.photobucket.com/albums/j248/87228/TgtGfx2.jpg

montrala
06-10-11, 07:37
Also using ATC - the more shots in group, the more info on real accuracy potential from weapon/ammo/shooter combo.

When I was writing article for gun magazine in Poland on accuracy improvement from manual barrel crown cutting (using Stag as example) Best comparison came from ATC calculations. I used TargetCalc on this time to make calculations. Due to ammo supply problems I used 5 shot groups, shot only one group from each ammo before mod and one group after mod (no "best group hunting").

Results looked like that (@100m):

Sako Speedhead FMJ 50gr - ATC: 32mm -> 27mm, gain 15%
Barnaul FMJ-BT 62gr - ATC: 49mm -> 52mm, gain -7%
American Eagle FMJ 62gr - ATC: 30mm -> 30mm, gain 0%
Federal Gold Medal Match HPBT 77gr. - ATC: 18mm -> 13mm, gain 27%

Obviously best gain was on match grade ammo and high quality FMJ ammo.

ColtJ
06-10-11, 11:38
Here is a quick and sloppy illustration of my last point. Please note that this is just an extreme example to highlight the differences between ATC and ES.

Using ES, these groups measure about the same. Using ATC, these groups are very different. Clearly, the first group is much better, and ATC shows it.

Group 1. ATC= 0.251 MOA
ES= 1.474 MOA

http://i82.photobucket.com/albums/j248/87228/TgtGfx.jpg


Group 2. ATC=0.700MOA
ES=1.519

http://i82.photobucket.com/albums/j248/87228/TgtGfx2.jpg

Thanks,

Although I understood this makes it a bit clearer.

QuietShootr
06-23-11, 23:36
How does this look? I tried to ask the question somewhere else and got nothing but ****ing smartassery about my shooting ability and knowledge level. I know the ES is over 1.5 moa, goddamn it, this is load development. What I'm looking at is the average, which looks to me like under .5 moa. Yes?

http://i794.photobucket.com/albums/yy229/QS762556/300data1.jpg

OMD
06-23-11, 23:47
I'm more interested in the results of the aforementioned manual barrel crown cutting? Link please : )

Travis B
06-24-11, 00:15
How does this look? I tried to ask the question somewhere else and got nothing but ****ing smartassery about my shooting ability and knowledge level. I know the ES is over 1.5 moa, ******* it, this is load development. What I'm looking at is the average, which looks to me like under .5 moa. Yes?

http://i794.photobucket.com/albums/yy229/QS762556/300data1.jpg

I saw a post in the EE that made me think of this. A rifle claimed 1MOA with a 5-shot group and 1.5MOA with a 10-shot group. The thing that concerns me is variance. ES doesn't really take this into account. The aforementioned rifle should be either a 1MOA or 1.5MOA rifle, right? Well it would be it variance was calculated. When we take into account how far the "flyers" are off the average (that extra .5MOA in my example) we take into account variance. If you're shooting a 5 shot group you'll probably have a tighter group, so why not weight the tight group into the calculation more heavily than the flyers?

Sure it has some kinks (without me/someone else sitting down and spending hours on an algorithm that would factor in spread, number of shots, SD, variance, statistical significance of group changes etc. etc.--mostly which would not be important to almost all shooters) but I can honestly see how ATC would be very useful.

I would personally like to see a simple algorithm that takes into account MOA and ATC. That way extreme spread is taken into account (with MOA) and also the density of the group is utilized (with ATC).

shootist~
06-24-11, 01:13
QuietShootr,

Is the Rem 700 a heavy barrel or hunting profile? If it's a lighter weight barrel, and the low flier was near the end of the string it could just be the result of a a hot barrel? Possibly a case where five shot strings with a cool down in between is the batter choice.

You definitely get points for a 10 shot group (with either) pushing a heavy bullet out of a magnum. The .5 MOA mean radius gives you an indication the load is close to working, I would think.

slomo
06-24-11, 05:35
ATC calculations mitigate the effect of fliers, but fliers are important. If a varmint hunter is shooting at a 4" target at 300 yds he needs a load that will deliver 1MOA Extreme Spread 100%. ATC is OK but ES is mandatory for a situation where one shot counts.

montrala
06-24-11, 08:54
I'm more interested in the results of the aforementioned manual barrel crown cutting? Link please : )

No link. I was published "on paper" in Polish gun magazine "Strzał" and guess what.... it's written in Polish :jester:

What do you want to know?


BTW If ATC (or Average Mean Radius) is .5 MOA that means to me that Average Mean Diameter of group is 1 MOA. So if we have AMD about 1 MOA and ES about 1.8 MOA we can assume that this rifle/ammo/shooter combo is capable of more-less 1.2-1.5 MOA shooting for practical reasons. This is of course non-scientific, and not too good for internet bragging rights, but outlines some practical capability.

P2000
06-24-11, 15:06
I shot my SR-15 with Battlecomp last week. 109 degrees and a bit breezy. At 100 yards with BH 69gr factory ammo.

http://i82.photobucket.com/albums/j248/87228/BH69grSR-15.jpg

ETA: This is the free version of OnTarget software.

BaileyMoto
06-25-11, 07:40
I think you have your work cut out for you..in regards to changing their minds about measuring groups. If the above group was presented to me and said to be ".5 MOA" - I'd be extremely confused. But, I'm stubborn. :P

For me, I feel it's important to know how 'wide' my groups is, if that makes any sense at all. I've also been using the more traditional method of measuring groups for nearly 20 years. So, well, that's just hard to deviate from.

If someone tells me "This gun shoots 1MOA", then my first thought would be that I should be able to put a quarter over their 100 yard groupings.

Either way, this makes some interesting discussion. :)

QuietShootr
06-25-11, 08:08
QuietShootr,

Is the Rem 700 a heavy barrel or hunting profile? If it's a lighter weight barrel, and the low flier was near the end of the string it could just be the result of a a hot barrel? Possibly a case where five shot strings with a cool down in between is the batter choice.

You definitely get points for a 10 shot group (with either) pushing a heavy bullet out of a magnum. The .5 MOA mean radius gives you an indication the load is close to working, I would think.

This is the rifle:
http://www.remington.com/products/firearms/centerfire/model-700/model-700-xcr-tactical-long-range.aspx

I honestly think the fliers might be me ****ing up, since I shot this at the end of a long day. Heat is likely not an issue, because I took 5 minutes or better between each shot.

tb-av
06-25-11, 09:36
If someone tells me "This gun shoots 1MOA", then my first thought would be that I should be able to put a quarter over their 100 yard groupings.

I agree. I've been reading this site linked below and it seems to me this guy is saying that ATC is "normal" because history has shown that people's intent when speaking of group size is to "throw out fliers" and that they are actually trying to express the smaller more dense group (sounds like a fishing story)

The problem I have with that is that not everyone thinks that way and more importantly in the real world fliers do occur.

There is a very simple solution to the issue. The Decibel is measured with the dB which means absolutely nothing on it's own. It's relative to something. So it is reported as dBu, dBv, dBSPL, dBFS, etc. and those indicators after dB allow everyone to know exactly what is being reported.

So it would be very simple to report MOAa or MOAes and everyone would be on the same wavelength.

I mean if I shot a gun for year and started out with .75 MOAa and 2.5 MOAes and by the end of the year I was at .40 MOAa
and 2 MOAes. I wouldn't feel right telling someone I could shoot groups the size of a finger nail when in fact I need a target the size of a camera lens.


http://www.bmotsoft.com/grpsz_p1.html#grpsz_p1_top

Cameron
07-12-11, 17:05
10 shots at 100yards from Daniel Defense built Lothar Walther barreled Recce.
16" LW50 1in7" twist with a Wylde Chamber
Black Hills blue box 50gr v-Max

ES: .711MOA
ATC: .281MOA

I just like the fact that all 10 shots fit inside a 1" square.

http://i886.photobucket.com/albums/ac61/gstuffnow/DanielDefenseTarget0711.jpg

shootist~
07-12-11, 17:30
That's an outstanding group, Cameron. I would be very interested to see how it does with heavy bullets, such as the 77 SMKs as well.

Cameron
07-12-11, 17:37
That's an outstanding group, Cameron. I would be very interested to see how it does with heavy bullets, such as the 77 SMKs as well.

Out of all the various ammo I have used, I seem to get the most consistent results with Federal Gold Medal Match 77gr SMKs...

Cameron

P2000
07-12-11, 19:13
Awesome group. ATC in the .2's!

twadsw01
09-08-11, 15:24
Attempting to make this the standard way by which we communicate the ability of a given rifle/ammo/shooter combination to group shots in the same location is a great idea.

As an engineer who designs products which need to adhere to certain accuracy/precision standards, I deal with tolerances on a daily basis (Gaussian distributions, standard deviation, means, etc.). When I started shooting factory ammunition - and, later, handloads - to search for the load which produced the smallest groups from my rifle, I initially measured extreme spread like everyone else, and kept a spreadsheet documenting my findings in an organized in graphical way, especially when searching for the correct handload recipe (making it easy to spot trends when varying bullet weight, powder charge, seating depth, etc., etc.).

However, I quickly found that measuring ES introduced much more "noise" into my data collection, due to fliers caused by, in many cases, range-session-to-range-session variation (e.g., what I'd eaten that day for lunch and supper, how much rest I'd gotten the night before, temperature at the range, how noisy the range was on a given night, how I was feeling at that particular range session, and on, and on). A group that was 0.4" in 4 shots would open up to 1" on the fifth shot, perhaps because of someone concurrently firing a 16" 30-'06 on the adjacent bench, or whatever the case might have been.

Therefore, I started using digital calipers to measure the "coordinates" of each shot's center-point from a defined origin on the target, then calculating the "center of gravity" for each group, and finally, calculating the distance from that center of gravity in a given group to each of the group's shots. I averaged all of these measurements and recorded that in the spreadsheet...voila. Average-to-center (a shooting application of the concept of "standard deviation"). Along with shooting a 10-shot "control" group of a known factory load from a single lot (FGMM 168gr), calculating it's ATC, and using this as my normalization factor when measuring, calculating, and recording the other groups' ATC's from a given night at the range, it yielded a much more consistent metric for quantifying accuracy for whatever load was under test. Those fliers due to various factors still would degrade the quantified accuracy, but nowhere near to the degree they did when simply using ES as an indicator of accuracy.

Great idea, guys.

twadsw01
09-08-11, 16:07
Exploring the idea of how to relate this new standard of measurement to the existing standard of using ES to estimate rifle/shooter/ammunition combination accuracy...

It is difficult to compare ATC to existing ES numbers. Some in the posts above have suggested doubling the ATC will yield a quantity that is more closely related to the ES numbers currently thrown around for comparing accuracy. I think this is a step in the right direction, but perhaps adding another factor in the mix will give a more complete story when relating this metric to others.

The ATC is a measure of the standard deviation of each shot from the center of a group. Another way of saying this is that it is also the length of the mean radius; an average of the lengths of the radii from the center of the group to each shot. Well, as a collection of radii, these also have a standard deviation themselves. I think that adding the ATC quantity to 2x the standard deviation of the radii themselves, then doubling that entire quantity would give a metric which more accurately measures overall accuracy, yet more closely indicates the largest possible group the rifle/shooter/ammo will produce (corresponding more closely to ES measurement).

What this number is, effectively, is the diameter of a circle which 95.4% of all shots taken by a shooter using a given rifle and ammunition combination will fall into. 95.4% comes from using two standard deviations of the average-to-center radius length.

Good idea, or am I over-complicating this? The reason for all this is that I think this number is more comparable to our traditional ES numbers, and gives a better idea than ATC alone of what we'd measure on a given day if we took a caliper to a group of shots on our targets.

Illustrated below...
http://i.imgur.com/mSTjc.jpg

shootist~
09-08-11, 17:09
IMO, a "good" ATC, and one that I see with my 77 SMK reloads, is ~1/3 or less of the ES. With me on the trigger and 10 shot / 100 Yd groups, I see ~1.5" ES with and ATC of < .5. A very satisfactory load for me and one that is also a proven load at the extreme range of the .223.

In theory you could have an ES of 1.5" and an ATC of 1.5" - a group with all shots falling at the outer edge of the pattern. The initial test load I tried in a 16" CL carbine with some MG 55s was not too far off this measure. The ES at a little over 2" was in reality a poor group, even though a "2 MOA" group for a carbine is considered pretty good.

I suspect that ES/MOA will continue to be the commonly used measure, however.

twadsw01
09-08-11, 17:19
Probably a good suspicion you have there, shootist - if you're doing those sorts of calculations (ATC, standard devs, etc.) by hand, it's a real pain, even with a spreadsheet that you can plug coordinates into. Nothing hard about it to understand, it just takes a while to do all of the measuring. It was definitely something that I got tired of quickly, and would be done over supper at the coffee table.

Your ES = ATC example would even yield similar results with my crappily-described method in the post above yours because the standard deviation of the ATC-radii would be zero if the shots were exactly on the edge of the circle the shot pattern forms.

Would be good to go through and collect some data for this - shoot a lot of groups (or measure groups previously shot), calculate ATC, ES, and whatever my modified metric would be called.

I think you're right though - the main method will probably continue to be ES, which can easily be measured by simply looking at the target and estimating. I guess that's that particular approach's real beauty and appeal.

P2000
09-08-11, 19:08
Exploring the idea of how to relate this new standard of measurement to the existing standard of using ES to estimate rifle/shooter/ammunition combination accuracy...

It is difficult to compare ATC to existing ES numbers. Some in the posts above have suggested doubling the ATC will yield a quantity that is more closely related to the ES numbers currently thrown around for comparing accuracy. I think this is a step in the right direction, but perhaps adding another factor in the mix will give a more complete story when relating this metric to others.

The ATC is a measure of the standard deviation of each shot from the center of a group. Another way of saying this is that it is also the length of the mean radius; an average of the lengths of the radii from the center of the group to each shot. Well, as a collection of radii, these also have a standard deviation themselves. I think that adding the ATC quantity to 2x the standard deviation of the radii themselves, then doubling that entire quantity would give a metric which more accurately measures overall accuracy, yet more closely indicates the largest possible group the rifle/shooter/ammo will produce (corresponding more closely to ES measurement).

What this number is, effectively, is the diameter of a circle which 95.4% of all shots taken by a shooter using a given rifle and ammunition combination will fall into. 95.4% comes from using two standard deviations of the average-to-center radius length.

Good idea, or am I over-complicating this? The reason for all this is that I think this number is more comparable to our traditional ES numbers, and gives a better idea than ATC alone of what we'd measure on a given day if we took a caliper to a group of shots on our targets.

Illustrated below...
http://i.imgur.com/mSTjc.jpg

That is a pretty awesome use of statistics! However, I think it serves a different purpose and is too cumbersome to simply measure precision. Using your method a statistician could make statements like "Under x conditions, a 1 foot diameter circle could be hit 87% of the time at 800m", giving soldiers an idea of what their equipment is really capable of. Pretty neat, but I would have no use for it. Trying to hit targets is another issue, with far more variables than just inherent precision of your equipment.

Part of the appeal of using the ontarget.com software and a 10 shot ATC is that it is very easy to do, and it is in my opinion the minimum necessary to evaluate precision. I think the role of this measurement is to do things like load development, comparing brand x ammo to brand y ammo, seeing if your new SPR is more accurate than your other rifle, see if your barrel really is starting to group poorly ect. That is it, just a simple tool to answer a question.

twadsw01
09-08-11, 19:33
I agree with you, P2k, on the basis of simplicity-of-measurement. I think that if you're using the ATC on your own (in a world of people who talk about accuracy using ES as their chief metric) as a way to compare ammunition, your rifle's track record over time w/ regards to accuracy, and the like, then there's no need for the extra calculation I described. Simply plug photos of targets into the software, easy as it gets, and you have a more meaningful indicator of "accuracy" than ES.

I think I was simply trying to figure out a way that our numbers figured using the ATC method could be put in terms that are more comparable to ES numbers people typically quote to describe their rifle's accuracy, their shooting ability, and/or their handload's accuracy. As some have pointed out, for people who have always measured groups by using ES, the ATC numbers don't really have any meaning until they've spent time own their own measuring their own targets this way. That way, they build up a little bit of an intuition around how ATC corresponds to ES.

All I've described in the above posts is pretty much a scaling-factor to apply to ATC to get something corresponding better with ES, although a little more informed than simply multiplying ATC by two. So, it's really no less useful than describing accuracy in terms of ATC - just more intuitive for people used to ES measurements. That's all. Still describes accuracy of the rifle/shooter/ammo combination, like ES and regular ATC do.

Biggest thing, as shootist said earlier, is that all of this is wayyy too complicated for people who don't want to photograph targets and import the photos into software for measurement. If that's off the table, then ES wins every time because of its simplicity.