Low ES and SD Give Worse Groups!

[DaveMarine1]

I am doing some load developement at 100yds and its going ok. I loaded 5 rounds of 168SMK and 44gr Varget with FGGM primers. One thing that I found though is that when I shoot a nice 1/4 inch 4 shot group (with one flyer to make it a 5 shot 1 inch group) the ES is around 30 and SD aout 17. Then as I continue the load developement with the same load just different primers, I shot a 1 1/2 inch 5 shot group but the SD was 10 and ES was 3 (if I remember correct). In theory wouldnt the lower SD and ES have better groups being the shots are more consistant as far as velocity? I am not putting too much thought into this, Im just wondering if anyone has any insight onto why this happens. I shot six 5 round groups with three different charges and three different primers and found that when the SD and ES where low, the groups were 1"+ but when the ES was around 30-35 and the SD was 15-17, the groups where nice and it seemed like one could work on that. Any info on this?

David

 

[Judd]

Shoot those same groups at 3-500 yards an you might get different results. I know my buddy has a 6mmBR that with 105's is a hammer at 3-500 yards but it won't shoot a decent group at a 100 to save his life. He now has a 80gr load to shoot at 100 and it is always less than .5 and I have seen 1-2 less than .25. I don't understand but he says it has something to do with a 100 yds with a 105 isn't far enough for the bullet to "go to sleep".

Good luck!

 

[nosualc]

You didn't say what distance you're trying to tune for (short vs. long). If your goal is 100, then focus on that; ES/SD are not as important as group size (witness BR guys who only drop charges).

If your goal is further distances, see how things group at 300+. Better ES and SD will give you less vertical dispersion at longer distances. You can't really judge things at 100yds as the difference in vertical will be insignificant relative to minor gun handling differences, etc.. This is a trap many of us fall into because 100yds is so much more accessible/easier.

Also, it sounds like you're changing lots of things (3 different charges, 3 different primers). Try focusing on changing only one thing at a time. It could be the load you're shooting with low ES/SD is faster/slower enough to get you out of an accuracy node.

-nosualc

 

[wapiti25]

AS some have already stated I'm happier with loads that are devoped at 300yds than 100yds unless it is for a 100yd match.

 

[DaveMarine1]

I see what you are saying, I am not getting too wrapped up in it but will definatly try some longer ranges with the load. It is mainly a short range load.

I saw that 44gr and 44.2 gr worked the best for me so I took 5 rounds of 44gr and 5 rounds of 44.2. I then tried 5 shots of 44gr with the FGGM primer, the CCI primer and the Tula primer. I then tried 5 shots of 44.2 grains with the FGGM primers, then CCI, then Tula. The FGGM gave me the best 100yd group with 30ES and arond 17SD or so. It also gave me the best 42.2 gr group with around a 12ES and a 3SD. I will have to try that out to 300 or so if I can.

 

[BoydAllen]

A friend who has a tunnel, and shoots longer ranges in competition, says that the loads that have done well at 100 have also done well at 600. I believe that low ES is a function of charge weight, case volume, ignition, and neck tension consistency, and at short ranges may not have much effect on group size. On the other hand, if you have these factors well in hand, and tune the load well, you should be able to have both low ES and good short range accuracy. IMO it is difficult to do as good, or efficient of a job of tuning if you are loading away from the range. Are you shooting all your groups with wind flags? Another thing to consider is that there are some that think that for any given rifle and load component combination (and probably seating depth) that tune is velocity specific. When you change something that changes velocity, and you are not aware that it has, you may incorrectly attribute the difference in accuracy to the component, when what has really taken place is more like what happens when you change the weight of the powder charge. Are you shooting over a chronograph?

 

[357Mag]

Dave M -

Howdy !

I have read results that show low SD/ ES won't necessarily render the best groups.
Yes... this sounds counter-intuitive; but many things in shooting/reloading are.

If you can arive @ a load that groups well w/ your gun...... " Why ask why " ?

With regards,
357Mag

 

[fr3db3ar]

I'm not the expert that some of these guys are, but I'd have to agree with the distance grouping. My AR308 will group 1 to 1.25" @ 100 but consistantly groups right around 3" @ 400 yards.

 

[jdfletch]

Dave,

Lower ES/SD groups do NOT always correspond to better groups. Better groups usually are more a function of barrel timing, i.e. - barrel position when the bullet leaves (not to be confused with aiming...). Barrels oscillate when shot, so you want the bullet to leave at the point of least dispersion, and that's at the top or bottom of the oscillation. There are several papers and calculators out there such as the following from Chris Long that explains optimal barrel timing.

http://www.the-long-family.com/OBT_paper.htm

Essentially, the easiest method for testing best OBT is to shoot a ladder test of loads in 1% grain increments of max (say 0.3gr for 6mmBR or 0.4gr for 308 Varget loads) at 300 yards or so. There will be several "nodes" where two or three of the loads shoot at the same point of impact (usually about 2 grains apart with my testing). That will be an OBT node. Note the velocities of those loads and that's where you'll want to stay while optimizing ES/SD with different primers, bullets, seating depths, etc. Note that changing powders will change the OBT due to internal ballistics, so you'll have to ladder test for each powder.

If you or a friend has a copy of Quickload, it can give you a very respectable quess for OBT if you put in your barrel and bullet dimensions properly.

The ladder test is simple and effective at finding the best grouping load. Be concerned more with vertical variation and not horizontal while doing the test. As stated before, low ES/SD numbers don't matter much in the short game. Also, they really don't matter much until you get out to 1000 yards shooting. Just look at the ballistic numbers for two bullets shot with an ES of 40...

Berger .308 155gr Hybrid (From www.jbmballistics.com)
2960fps 300 yards = -3.6MOA, 600 yards = -12.1MOA, 1000 yards = -29.4MOA
3000fps 300 yards = -3.5MOA, 600 yards = -11.7MOA, 1000 yards = -28.5MOA

Hope this helps....

Doug

 

[rcw3]

Dave,

Lower ES/SD groups do NOT always correspond to better groups.

. . . . . . .

. . . . . . .

Hope this helps....

Doug

Doug

I think you are right on the money there. The trick for long range is to try to get a load that is both accurate and has low ES and SD numbers. For short range I don't think low ES and SD are a big deal but definitely so for long range loads.

Robert

 

[amlevin]

I've found that I pay more attention to Mean Absolute Deviation rather than the ES or SD.

When I started doing that there was more of a correlation of groups to data.

ES can be high with just ONE shot that is "way out there". This too can skew the Standard Deviation. The MAD is, to me, more meaningful as it shows how close the individual shots in the dataset are to the average.

I use the chronograph data pretty much to create my ballistics "cheat sheet" for changing distances.

 

[Win94ae]

I it so odd that there are so many that look at load development in so many different ways.


I use the Audette Ladder Test to load develop; there are two things to look for in my ladder. One is to note the position of the shots. Second, is to note the velocity spread.

Close impacts at 100 yards will revel when the barrel's harmonics/vibrations are nearest the throat.

Close velocities are a sign that the powder is hitting a plateau whereas the powder burns most uniformly, due to numerous variables.

The powder burning uniformly is not effected by, and does not effect barrel harmonics.

When one load develops at 300 yards, it is easier to know when ES jibes with barrel harmonics because only then will you have close impacts.


This link is a response on the "go to sleep" notion.
Epicyclic Swerve

Just to be clear about the conclusions of the modeling: The phenomenon of smaller angular groups at longer ranges was not disproven. The only thing I've shown is that if the phenomenon actually happens, epicyclic swerve is not the cause of it.

I blame parallax for the perplexing "smaller angular groups at longer ranges" anomaly.

 

[JCummings]

Group size is function dispersion due to both velocity variation and barrel harmonics. Why would you expect the charge with the lowest ES and SD to necessarily also time the bullet to leave the barrel at this optimal phase of its harmonics?

 

[jsthntn247]

I would go with the primers that were giving lower ES numbers and work up a load with them. There is something about the combo that your gun likes, you just might have to play with seating depth and powder charge to find out what that is. However, if your not shooting over 400 yards consistently I wouldn't bother wasting the time, bullets, and powder.