Use lowest SD or lowest MOA?

[Forrest Mc]

Hello all, I am trying to improve my new reloading skills and have been shooting lots of groups with various combinations looking for a solid 140 g. performer. I think I just shot the best I can do, but question whether to go with lowest SD group or best moa group.
Two days ago at the range testing the 6.5 CM with 5 shot groups,
Using a LabRadar, the best results I got were:
42.3 gr H4350 - ES 7, SD 2.6, avg 2807 fps, .39 moa
42.6 gr H4350 - ES 10, SD 3.8, avg 2821 fps, .32 moa

My gut tells me to go with the SD 2.6 load and work on distance to lands. I appreciate your input, thanks

Bud

 

[CharlieNC]

Neither of those results are statistically different. The most reliable method involving only a few shots is to run an Audette charge ladder, which you can Google and download.

 

[Ol’ Ed]

In regards to your “trying to improve my new reloading skills” your ESs and SDs indicate that you’re heading in the right direction! If you are a new reloader, you’re doing great! As to the rest of the results you shared, I’d like to know the intended use of this rifle, plus a picture of your targets. Having the last two pieces of info would, to me, be helpful.

 

[Forrest Mc]

Thanks Ol' Ed,
The rifle (Savage 12FV) is for long range targets, steel, and occasional varmints. Hope the pic attaches.
This load is for targets

 

[Ol’ Ed]

You and I do targets the same way! Given the application, I’d go with the 42.6 grain, .32 moa loads and tweak the seating depth to wring out as tight a group as possible. And then I’d just enjoy shooting the rifle (isn’t that really the bottom line?). I have “better than 1/4 moa” rifles that vary by 20+ ES (some is the error in my magneto V3, too, I’m sure), so don’t get too hung up on ES and SD. As you’ve undoubtedly seen repeated on this site many times, it’s the information that you get from the target that really matters. Shoot, enjoy, and repeat often! Then buy another rifle and do it all over again!

 

[Dusty Stevens]

Find your best group, load some more to see if it repeats next trip, then on the next trip if it repeats again drag out the chrony but not before then. ES has nothing to do with good aggs no matter how much we want it to

 

[Zero333]

I agree 100% with Dusty.

I used to chrono during load testing, and it did nothing but confuse things.

Now, I ONLY use the chronograph once I have a solid load that shoots consistently the same on different days.

Looking at both your groups ( 42.3 & 42.6 gr ), even if their size was reversed, I would pick 42.6 gr because it has less vertical dispersion.

As a side note. If you want to know more realistic ES and SD numbers, you have to shoot a minimum of 10 shots.

In a 10 shot string if you get single digit SD, then that's good enough as long as every 10 shot string shows single digit SD.

 

[AJC]

Find your best group, load some more to see if it repeats next trip, then on the next trip if it repeats again drag out the chrony but not before then. ES has nothing to do with good aggs no matter how much we want it to

So I drank the cool aid. So are the numbers useful for troubleshooting if your target sucks.

 

[dsculley]

For me, the target is the final arbiter. I primarily use my chronograph to watch for over pressure. I use the OCW method, and based on that premise 42.6 & 42.9 have nearly identical POI centers. I would test from 42.5 to 43 in 0.1gr increments to see if it is repeatable and to find the center of the node. I would then test for seating depth using the Berger method, a coarse test first followed by incremental testing to find the best depth (testing for seating depth in pretty much the same way you do for powder). As an aside, I test for seating depth first with a mild load (my starting load), then test for powder charge, then fine tune seating depth. I have seen changes in seating depth open up/close my groups more than changes in powder charge.

At this point, I would test at the longest range available to verify at distance. (If I were doing the testing, I would also load several rounds 0.1gr above & below my selected charge to see if they do in fact shoot within group from the selected charge. (I know from testing that I can do this with my load and still shoot less than 0.5 moa at 287 yds, the longest range I have readily available.)

If your test is repeatable and you find the center of the node you will not only have a good load, but a forgiving load as well.

Scott Satterlee developed the method using chronograph data, primarily SD, to locate a node. He says it works well for him, but I don't usually find my best load having the lowest SD. YMMV.

 

[Dusty Stevens]

So I drank the cool aid. So are the numbers useful for troubleshooting if your target sucks.

No. There is not a correlation between the best load on target and the chrono. I cant think of a single instance that a low es was the best load.

 

[Forrest Mc]

I appreciate the input from you all. Definitely food for thought. Thank you.

 

[Rust]

At 100 yards ES/SD aren't all that important. At 1,000 yards ES/SD are critical.

Numbers I have at hand (old data pretty close): a 140 gr A-max at 2,900 fps drops 297 inches; at 2,800 fps drops 322 inches. That is 5 inches of vertical for every 20 fps difference in velocity. Wind drift is affected by velocity to a lesser degree, a little less than 1 inch per 20 fps in a full value 10 mph wind.

At 600 yards that 100 fps difference in velocity in vertical is about 6 inches, or about 1.2 inches per 20 fps, not nearly as drastic.

You've got good ES/SD numbers to start with. This indicates you have good loading skills to begin with. Now it's a matter of fine tuning your load and maintaining uniformity from round to round.

Don't fret chasing high velocities, a slower velocity hit is always better than a higher velocity miss.​

 

[Forrest Mc]

Maintaining uniformity is my goal. The bullet seater I use for the 6.5 achieves the concentricity I expected, but the seating depths vary too much, in my mind. What are your thoughts on the Wilson seater w/micrometer to help get to the seating consistency? Hypothetically, all other variables staying the same on the above results, would .005" accuracy in seating depth improve ES/SD for 1000 yard shooting?

 

[Howland]

Both groups look good. With five shot groups I don't pay much attention to SD but ES does concern me. Mine, not yours. Both are fine but a larger sample would give me more confidence.

You could do one of two things. Pick one and run with it or load up twenty or thirty of both and put them on paper at various distances. Both sets would likely be more than acceptable, but a dealbreaker would be if either exhibited vertical stringing at the furthest distances. With a sample size of twenty or thirty an SD would have validity with target results to back them up.

 

[miningshawn]

I agree 100% with Dusty.

I used to chrono during load testing, and it did nothing but confuse things.

Now, I ONLY use the chronograph once I have a solid load that shoots consistently the same on different days.

Looking at both your groups ( 42.3 & 42.6 gr ), even if their size was reversed, I would pick 42.6 gr because it has less vertical dispersion.

As a side note. If you want to know more realistic ES and SD numbers, you have to shoot a minimum of 10 shots.

In a 10 shot string if you get single digit SD, then that's good enough as long as every 10 shot string shows single digit SD.

What caliber\case would you expect to see single digit SD? It seems impossible in .223, but .308 is easy. Where is the break and is caliber part of the equation?
Thanks in advance,
Shawn

 

[Nightraider]

At 100 yards ES/SD aren't all that important. At 1,000 yards ES/SD are critical.

Numbers I have at hand (old data pretty close): a 140 gr A-max at 2,900 fps drops 297 inches; at 2,800 fps drops 322 inches. That is 5 inches of vertical for every 20 fps difference in velocity. Wind drift is affected by velocity to a lesser degree, a little less than 1 inch per 20 fps in a full value 10 mph wind.

At 600 yards that 100 fps difference in velocity in vertical is about 6 inches, or about 1.2 inches per 20 fps, not nearly as drastic.

You've got good ES/SD numbers to start with. This indicates you have good loading skills to begin with. Now it's a matter of fine tuning your load and maintaining uniformity from round to round.

Don't fret chasing high velocities, a slower velocity hit is always better than a higher velocity miss.​

This

You can't build a house on a dirt base without it creating issues. The same is true in reloading. If you build a beautiful house (100y groups and not ES/SD based data) but neglect the foundation, no matter how nice the house, it'll far apart in the long run. If you build a solid foundation (based on ES/SD and powder nodes) and then build a beautiful house (tuning the OAL) it'll last until something drastically changes (throat erosion, hardened brass, new lot of components). Most of all very rarely does a 100y group translate into the same thing at distance so tune at whatever distance you're planning on shooting.

 

[dcali]

Three things -

Don't use the best results to pick a load. Use the average results. Using the best group is just going to leave yous catching your head when you can't reproduce it. Average results are going to be more representative of what you'll actually see. Some worse, some better. IF you use your best, you can pretty much guarantee that when you go out and shoot for real, you'll only rarely do that well. Depending on your application, you might even consider using your worst result, which would tend to be a conservative group size that you can expect in competition/the field.

Depending on how many groups you shot to get to those results, they may or may not be statistically significant. It's fine to get a feel for things with a small number of shots as you run tests - huge groups aren't going to get smaller by shooting more. But when you get to two loads that are close, you're going to need to shoot more than a couple five shot groups to tell them apart. Depending on your disicpline/usage, you might be done - just pick one and go shoot. If you're hell bent on getting down to the exact optimum, you're going to have to shoot. There are reasonable limits to this (money, time, barrel life, etc), so you need to balance confidence in your load with the cost of getting that confidence.

Velocity SDs are like group sizes - a few shots doesn't tell you anything reliable. The good news is that SD takes every shot into account (instead of the two most extreme shots, like group sizes do). This means that if you shoot five 5-shot groups of the same load (for example), and measure the velocity of every shot, you can get an overall SD based on the full 25-shot sample, which should be fairly reliable. You don't have to separate it out int five 5-shot SDs and then trying to figure out how to interpret that.

 

[Forrest Mc]

Well, after everybody's help and encouragement, a load was developed with 42.6 gr H4350, seating a 140 gr ELD M with .005 jump. I packed up and went to my first F-Class match and did not embarrass myself even though finishing last. I am switching to Hybrid Target bullets so the load development will start over.

 

[JFrank]

So I drank the cool aid. So are the numbers useful for troubleshooting if your target sucks.

No

 

[David Christian]

@Forrest Mc, looks like you are on the right track. Not to confuse things, but if you are into data and want to combine chrono numbers along with group size, read this article, watch the video, download the excel spreadsheet, enter your numbers and then see where the graph demonstrate your best node. From there you can work on seating depth.

https://www.65guys.com/load-development-analysis/

Here is an example from one of my tests.


Also, are you using one of these? I found that this fixed the variability in my seating depth.

https://www.midwayusa.com/product/1...er-die-vld-bullet-seating-plug-drift-assembly

Good luck!
DC