Group size: Moving towards using 10 shot ATC instead of ES

[montrala]

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]

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




Group 2. ATC=0.700MOA
ES=1.519

Thanks,

Although I understood this makes it a bit clearer.

[QuietShootr]

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?

[OMD]

I'm more interested in the results of the aforementioned manual barrel crown cutting? Link please : )

[Travis B]

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?

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~]

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]

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]

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

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]

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



ETA: This is the free version of OnTarget software.

[BaileyMoto]

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.