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Smallest group or smallest SD?

Billiam1211

Billiam1211

Gunny Sergeant
Full Member
Minuteman
Feb 19, 2018
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#1
Just looking for insight from more experienced reloaders. I have a Tikka Tac A1 that I've started load development for since replacing the barrel. It's 6.5CM w/ a 26-inch RockCreek PVA prefit. This is a PRS match rifle so shooting is typically 100yd-1,000yds. All load work ups were done with a MagnetoSpeed and shot @ 200 yards. Groups were shot WITHOUT the chrono attached.

I did an initial Satterlee test with Hornady Brass and found the flat spot to be 42.0 grains of H4350. Did a seating depth test to tighten up accuracy and found that 2.825" produced best accuracy which is 65 thousands off the lands. This load is able to shoot groups at .3MOA regularly 1/2 MOA on off days. I found my summer time velocity to be 2,796fps (70 Degrees F) and on Sunday I chronograhed 10-shots and got a velocity of 2,786fps (16 Degrees F). My standard deviation has been consistently 12-15 fps. The first photo below is from this load.

Did the same exact test above, however I switched over to Peterson Brass just to see what would happen. With the Peterson I found the velocity flat spot to be at 41.7gr H4350, which got my 2,830 fps and a SD of 4. With this loading all my groups were 1/2 MOA, nothing better, nothing worse. 2nd Picture shown. 2nd Photo is the Peterson load.

I'm thinking I'm just going to stick with Hornady brass for now because I keep printing spectacular groups, however I'm interested to see what other people think.

Thanks!
 

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#2
Billiam1211 said:
Just looking for insight from more experienced reloaders. I have a Tikka Tac A1 that I've started load development for since replacing the barrel. It's 6.5CM w/ a 26-inch RockCreek PVA prefit. This is a PRS match rifle so shooting is typically 100yd-1,000yds. All load work ups were done with a MagnetoSpeed and shot @ 200 yards. Groups were shot WITHOUT the chrono attached.

I did an initial Satterlee test with Hornady Brass and found the flat spot to be 42.0 grains of H4350. Did a seating depth test to tighten up accuracy and found that 2.825" produced best accuracy which is 65 thousands off the lands. This load is able to shoot groups at .3MOA regularly 1/2 MOA on normal to bad days. I found my summer time velocity to be 2,796fps (70 Degrees F) and on Sunday I chronograhed 10-shots and got a velocity of 2,786fps (16 Degrees F). My standard deviation has been consistently 12-15 fps. The first photo below is from this load.

Did the same exact test above, however I switched over to Peterson Brass just to see what would happen. With the Peterson I found the velocity flat spot to be at 41.7gr H4350, which got my 2,830 fps and a SD of 4. With this loading all my groups were 1/2 MOA, nothing better, nothing worse. 2nd Picture shown. 2nd Photo is the Peterson load.

I'm thinking I'm just going to stick with Hornady brass for now because I keep printing spectacular groups, however I'm interested to see what other people think.

Thanks!
Click to expand...

Was this Peterson brass NEW or 1X or 2X fired??? I'm wondering about case volume change with the Peterson brass???
 
#4
I like tight groups would not care if the sd was 30 if all my hits were like the first group on the left Id be a happy camper . My chances are the high sd groups would look more like the right pic . I have a lot of flaws in my shooting enough that even low sd reloads really don't make up for my mistakes . but that is me . good luck finding that mix that makes it all worth it to you .
 
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#7
Billiam1211 said:
Just looking for insight from more experienced reloaders. I have a Tikka Tac A1 that I've started load development for since replacing the barrel. It's 6.5CM w/ a 26-inch RockCreek PVA prefit. This is a PRS match rifle so shooting is typically 100yd-1,000yds. All load work ups were done with a MagnetoSpeed and shot @ 200 yards. Groups were shot WITHOUT the chrono attached.

I did an initial Satterlee test with Hornady Brass and found the flat spot to be 42.0 grains of H4350. Did a seating depth test to tighten up accuracy and found that 2.825" produced best accuracy which is 65 thousands off the lands. This load is able to shoot groups at .3MOA regularly 1/2 MOA on normal to bad days. I found my summer time velocity to be 2,796fps (70 Degrees F) and on Sunday I chronograhed 10-shots and got a velocity of 2,786fps (16 Degrees F). My standard deviation has been consistently 12-15 fps. The first photo below is from this load.

Did the same exact test above, however I switched over to Peterson Brass just to see what would happen. With the Peterson I found the velocity flat spot to be at 41.7gr H4350, which got my 2,830 fps and a SD of 4. With this loading all my groups were 1/2 MOA, nothing better, nothing worse. 2nd Picture shown. 2nd Photo is the Peterson load.

I'm thinking I'm just going to stick with Hornady brass for now because I keep printing spectacular groups, however I'm interested to see what other people think.

Thanks!
Click to expand...

What's the extreme spread of each of those loads?
 
#10
Billiam1211 said:
Ahh, I forgot to mention that!

Peterson brass was brand new and I ran it through a FL Body Die and Neck die.
Hornady Brass has been fired 6x and has been neck-sized with .002 neck tension.
Click to expand...

Even when FL sizing of new brass, new brass goes through changes from base to mouth as it forms to your chamber. If you were to measure the new cases that were sized to the 1X fired sized cases, you're very likely going to see a good change in volume on the up side. So, now that you fired the Peterson brass once, you might want to fire them again with that same load and then compare what you get.
 
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#12
Here's the deal........... in PRS a person doesn't shoot for groups; they shoot for hits across varying distances. Each load is only as good as it's worst group. so the first load is still a damn 1/2" load.

Go w/ load #2............ and it's a little faster.
 
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#13
C.R. Adams said:
Here's the deal........... in PRS a person doesn't shoot for groups; they shoot for hits across varying distances. Each load is only as good as it's worst group. so the first load is still a damn 1/2" load.

Go w/ load #2............ and it's a little faster.
Click to expand...

This definitely crossed my mind... unfortunately I think I have an unhealthy obsession with shooting small groups :rolleyes:. I crunched the numbers and there's barely any difference in the drop data until you get to about 700 yards. Most matches are 600 and in so I'm definitely going to load up 100 rounds with the Peterson brass and shoot a match at some point this year to see what happens.
 
#15
Remember also that even though H4350 is a VERY temperature stable powder, even from 15 F to say 90 F is going to make some difference here in all aspects. Point being, don't expect the same results in the summer regardless of powder choice.

H4350 is average .4 FPS per degree F across most lots.
 
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#16
AIAW said:
Remember also that even though H4350 is a VERY temperature stable powder, even from 15 F to say 90 F is going to make some difference here in all aspects. Point being, don't expect the same results in the summer regardless of powder choice.

H4350 is average .4 FPS per degree F across most lots.
Click to expand...

Yeah sounds about right. Given my data is a little crude I had a 10fps swing from 16 degrees F to 70 degrees so it’s in that ballpark.
 
#17
What your are describing and your results aren't adding up. If you really want some confidence with what you are describing than statistically you need to shoot a minimum of seven 5 shot groups for each load and brass combo. Enter your data project in the link provided and you will see if the differences are material or not. Or just go with what you happen to like, which looks like Hornady.

 
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#18
I’d take group 2 for PRS style shooting (targets almost never smaller than 1 MOA) but at 600 it’s kind of a wash. Past that I think you’ll find the first load will throw stray vertical shots, and those misses will feel vary random and frustrating. Did you try tweaking the seating depths on load two to tighten the group up?
 
#22
I had a 6XC years back and a load for it. It shot 1/2moa on paper at 500 and a little more out to 1k (under match conditions).
Never chrono’d other than a quickie to get an avg speed to tweak my guesstimating app.

I did later that year shoot it over an Oehler and was told that load sucks as the SD was in the mid-high twenties. Until I that barrel shot out that load shot 1/2-3/4 moa easily.

I miss the days when you never saw pictures of chrono screens....

A guy outside of Kingsville TX beat a little concept into my thick skull years ago:
-“believe the bullet.”
 
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#23
I agree with the guy that said to shoot it at distance. Sometimes boat tail bullets take a little distance to “stabilize”, for lack of a better word. The 6cm I just built will shoot 1/2 moa at 100 but will shoot 1” groups at 500 and I ain’t even that good of a shot. I have been using 400-500 yards to get a good idea of what the loads are doing On recent load development tests. Honestly either load you have there looks good though.
 
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#24
I shot a fluke group the other day over 5 shots with a SD of 1.4 and ES of 3 with a FPS of 3015, running 115 DTACS. However, the next time I checked it, which was several days later, it was 5 SD and 9 ES but FPS was on par with the previous test. I don't put much stock in 100 yard groups anymore. I wanna know what the bullet is doing at distance. We went out last week and tested at distance, checking our elevation with what our Kestrel was saying. With the DTACS, I didn't have to adjust anything all the way out to 1100, which is as far as we shot. I've always heard anything under 20 is good, but if my rifle is grouping at distance, I don't really care what the SD and ES is.
 
#25
My biggest issue is that there are no ranges near my area that go beyond 200 yards. What I've been doing is just taking the load that prints the smallest groups, then shooting 10-shots over the chronograph to confirm velocity. Then I would roll up to matches with good data and for the most part it worked fairly well. This year I wanted to improve and actually true up my data.

Since I have no ranges close by, I signed up for a match in southern indiana where they shoot out to a mile. My plan is to use this is an opportunity to true up data out to distance and write down what dope I need to hit and completely ignore the clock (MD says this match is mostly prone except a few PRS style stages). They said that after the match there's typically an open shoot as well so I'm going to bring both of my loads and test them at 600 for accuracy.
 
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#26
Billiam1211 said:
My biggest issue is that there are no ranges near my area that go beyond 200 yards. What I've been doing is just taking the load that prints the smallest groups, then shooting 10-shots over the chronograph to confirm velocity. Then I would roll up to matches with good data and for the most part it worked fairly well. This year I wanted to improve and actually true up my data.

Since I have no ranges close by, I signed up for a match in southern indiana where they shoot out to a mile. My plan is to use this is an opportunity to true up data out to distance and write down what dope I need to hit and completely ignore the clock (MD says this match is mostly prone except a few PRS style stages). They said that after the match there's typically an open shoot as well so I'm going to bring both of my loads and test them at 600 for accuracy.
Click to expand...

Where you located at? There is a range in Hazard, Kentucky called The Deplorable Rifleman's Club that goes out to 1600. You can go use the range whenever you like as long as there isn't a match going on. We have prone matches every first Saturday of the month, and there will be a handful of PRS matches there this year. The prone matches are shot at plate racks sitting at 400, 500, 810 and 1000 yards. 10 shots each plate with plates scoring from 5 points on the smallest to 1 point on the largest. Steel is always out at 810, 1000 and 1600. Don't know how long a drive that would be for you.

You can check their FB page out for more information. Just search for The Deplorable Rifleman's Club.
 
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#27
gasrat said:
Where you located at? There is a range in Hazard, Kentucky called The Deplorable Rifleman's Club that goes out to 1600. You can go use the range whenever you like as long as there isn't a match going on. We have prone matches every first Saturday of the month, and there will be a handful of PRS matches there this year. The prone matches are shot at plate racks sitting at 400, 500, 810 and 1000 yards. 10 shots each plate with plates scoring from 5 points on the smallest to 1 point on the largest. Steel is always out at 810, 1000 and 1600. Don't know how long a drive that would be for you.

You can check their FB page out for more information. Just search for The Deplorable Rifleman's Club.
Click to expand...

I currently live in . . . (dramatic pause) . . . Chicago :censored: I shoot the matches at a club in Waterman, IL and try to get up to Wisconsin for a few different clubs that hold PRS matches and even night time matches. I'm hoping to do the Barrel Maker Classic this year as well. My goal is just to get my rifle squared away for the longer distance stuff prior to Border Wars and all those series starting up.
 
#28
Billiam1211 said:
I currently live in . . . (dramatic pause) . . . Chicago :censored: I shoot the matches at a club in Waterman, IL and try to get up to Wisconsin for a few different clubs that hold PRS matches and even night time matches. I'm hoping to do the Barrel Maker Classic this year as well. My goal is just to get my rifle squared away for the longer distance stuff prior to Border Wars and all those series starting up.
Click to expand...

Hell, just walk out in a long alley and practice then. From what I hear, the gunfire wouldn't be a cause for any alarms up there.
 
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#29
gasrat said:
Hell, just walk out in a long alley and practice then. From what I hear, the gunfire wouldn't be a cause for any alarms up there.
Click to expand...

LOL that's very true. I could actually walk to Lake Michigan and practice on gulls. The windy city is a disaster though, don't even get me started.
 
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#31
For PRS, you're looking to best SD/ES you can get. If you're about 1/2 MOA group, that is way more than what you gonna need in a match.
ALSO, Peterson brass change a lot between their first fire and your reload, trust me it's a big change. My group with new Peterson were about 1/3 MOA with really amazing SD. On second and third I got 1 MOA group but still good SD. The solution I found: playing with neck tension. I added some tension with a bushing 0.020 tighter and got back to 1/4-1/2 MOA group.

Good thing to explore with your Peterson.
 
#32
sab567 said:
For PRS, you're looking to best SD/ES you can get. If you're about 1/2 MOA group, that is way more than what you gonna need in a match.
ALSO, Peterson brass change a lot between their first fire and your reload, trust me it's a big change. My group with new Peterson were about 1/3 MOA with really amazing SD. On second and third I got 1 MOA group but still good SD. The solution I found: playing with neck tension. I added some tension with a bushing 0.020 tighter and got back to 1/4-1/2 MOA group.

Good thing to explore with your Peterson.
Click to expand...


I ran into an issue with once fired Lapua vs new. My load sped up 30 fps when going to once fired and the rifle grouping opened up. Backed the charge down to get back into the 3013-3015 range, and my grouping came back. Only thing I can think of is neck tension. I don't know what was on the new, unsized Laupa. I run 0.020 on fired brass. SD and ES went up a little, but was still very acceptable for PRS matches.
 
#35
sobrbiker883 said:
I had a 6XC years back and a load for it. It shot 1/2moa on paper at 500 and a little more out to 1k (under match conditions).
Never chrono’d other than a quickie to get an avg speed to tweak my guesstimating app.

I did later that year shoot it over an Oehler and was told that load sucks as the SD was in the mid-high twenties. Until I that barrel shot out that load shot 1/2-3/4 moa easily.

I miss the days when you never saw pictures of chrono screens....

A guy outside of Kingsville TX beat a little concept into my thick skull years ago:
-“believe the bullet.”
Click to expand...
I hear you screaming. All this stuff and then someone wins a big match with factory ammo or handloads with zero development. What happens down range is what counts.
 
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#38
How are you throwing the powder? Does the slightly lighter powder charge into the Peterson Brass throw more consistently?

Personally I would repeat the test and compare the result. Were both the Hornady and Peterson loads shot on the same day? Also, how are you shooting the groups without the Chrono attached? are the holes made in the targets caused by the same bullets that you chronographed?
 
#41
Well I shot the Indiana 1 mile match this weekend and took my Hornady load that had the tight groups but SD of 15 to the match.

I was able to connect for the first time at 1,000 yards, 1,200 yards, and 1,300 yards. The down side is everyone was definitely right about taking the load with the lower SD. At the 1,000 yard line they had an array of targets. I told the spotter I didn't care about my score for the stage but wanted to get centered up on a 66% IPSC so that I could true up my data. I got on and connected a few times. By adjusting the Axial Form Factor variable I was able to true up my data really close for 100-1,200 yards. At 500 yards I cleaned the KYL rack no problems, however the targets beyond 1,500 yards were a shit show for me. The ROs kept telling me that my wind hold was perfect but I was over and under the target. That said, I think moving forward I'll shoot whatever ammo I have loaded and make a switch over to the Peterson load with the low SD.
 
Last edited:
#42
TripleBull said:
ES is often on the order of 3X the SD if you shoot 10 shots.

This article is worth the read:

precisionrifleblog.com

How Much Does SD Matter?

As long-range shooters, we tend to obsess over every little detail. After all, we’re trying to hit r...
precisionrifleblog.com precisionrifleblog.com
Click to expand...

Except the author is placing a 95% confidence level on 10 shots based an unknown population size. This is not statistical sampling at all. At best it is a random sample of an unknown population with no confidence. Chances are when you get up to statistical sample territory the outcome is going to be worse than the 68% bell curve in the article. In fact, it gets worse over time, which is a known variable as we reload and send more rounds down range. It is a game of deminishing returns. To think your standard deviation is sound with just 10 rounds is just stupid is as stupid does. The following claim should be our first clue...

"...we can use our 10 shot sample to estimate what the distribution would actually be if we fired 1,000 rounds..."

First thing there is no sample. That is testing a population of 10. If you just happen to have 100 rounds loaded than you have a sample of 10 out of 100. Your results are based only on that population. 100 items of interest is not even close to a minimum population to even consider sampling. Not some future imaginary 1000 rounds as well. You either have a tangible population of 1000 or you don't. If you want 95% confidence it will take a much larger sample than 10. And it is just representative for that population with no further wear and tear on the rifle. It is an in the moment set of calculations.
 
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#43
Culpeper said:
Except the author is placing a 95% confidence level on 10 shots based an unknown population size. ...
Click to expand...

In the context of the OP, I believe the linked discussion is worthwhile. If you want as much data as possible, chrono every shot and get your representative sample. If you want to spend all your time and barrel life generating stats, you are free to do so. For our ELR shooting, we pretty much do exactly that. If you chrono every round across the life of a barrel, you will document change in the average and the variation, but without periodic readjustment of the load, jump, etc, what does that mountain of data get you?

In the context of this thread, the bottom line - to me at least - is how the load shoots. I would not draw huge significance to the OP's comments about 0.3 to 0.5 MOA groups for the Hornady brass versus 0.5 for the Peterson. I'd scratch my head a little over the SD comparison and then maybe collect some data unrelated to MV if I was so motivated, because in the limited info posted by the OP, SD does not correlate with group size. Some aspects of the OP were apples to oranges, so go figger. How many variables would you allow to enter a comparison, like 1st shot on virgin brass versus 6th on the Hornady when SD is the focus of your comparison?

I've spent decades working with huge data sets and have worked with engineers and statisticians that are world class, but statistical conventions can lead you down the rat hole if you pick the wrong piece of data to obsess on.
 
#44
Culpeper said:
If you want 95% confidence it will take a much larger sample than 10.
Click to expand...
Are you sure about that? Based on what I have read, there is nothing stopping you from calculating a 95% confidence interval for a 10 shot sample, it is just that the interval is large and will most likely overlap and thus not tell you anything.

Ex
Power Charge A: SD 5, Sample 10, 95% confidence: [3.439 , 9.128]
Power Charge B: SD 25, Sample 10, 95% confidence: [17.196 , 45.640]
No overlap so you can be 95% confident that powder charge A is better then B.

Unless I am using the wrong calculator or interpreting the data wrong, which is certainly possible.

I used: http://www.statskingdom.com/40_confidence_interval.html
 
#45
Haven’t read all the responses. But I look at ES.

You an have a low SD and a high ES, but can’t really have a low ES and high sd. If that makes sense.

I also look at the ES over nodes of powder charges.

For example:

32.0 25 ES
32.2 6 ES
32.4 20 ES

vs

34.0 15 ES
34.2 12 ES
34.4 16 ES

I’m not picking the 32.2 because it has the lowest ES. I’m picking 34.2 because it is in the middle of the most stable ES in a series and an ES that’s within my acceptable range.

Then you will do seating depth tests to get your group size down. Followed by another powder test in .1gr increments to finalize the actual load.

So, both sd/es and group size matter. But at different stages of the development process.
 
#46
For another example, here is some ES testing I did last month.

You’ll notice and ES of 4, 2, and 5 that I didn’t care about as well as SD of 0.0, 2.2, and 1.7.

Because they were no in a stable node. The minute anything changes (environment or internally), and I’m gonna be out into one of the other more unstable areas.

I can post that chart without explanation and 80% of people will pick out the 0.0/2 sd/es and be all over it.

Just like I could post pics of seating depth test and people would pick out the .1moa with a .5 moa on either side instead of the .2moa that was consistent .2 on either side.

C2CF9637-8269-4AAF-BDC0-11D3197FD765.jpeg
 
#47
_Raining said:
Are you sure about that? Based on what I have read, there is nothing stopping you from calculating a 95% confidence interval for a 10 shot sample, it is just that the interval is large and will most likely overlap and thus not tell you anything.

Ex
Power Charge A: SD 5, Sample 10, 95% confidence: [3.439 , 9.128]
Power Charge B: SD 25, Sample 10, 95% confidence: [17.196 , 45.640]
No overlap so you can be 95% confident that powder charge A is better then B.

Unless I am using the wrong calculator or interpreting the data wrong, which is certainly possible.

I used: http://www.statskingdom.com/40_confidence_interval.html
Click to expand...

You're thinking. But...

Since the population's σ is not known the formula uses the T distribution with n-1 degrees of freedom: you're comparing the confidence across samples with a population unknown. This is what I'm referring to.

Normal approximation
Confidence interval: [0.00500450 , 0.494995].
Alternatively: 0.250000 ± 0.244995
The normal approximation requires a large sample size, as a rule of thumb at least 30.

There is a huge difference between random sampling and statistical sampling. If you believe political polls than you like random sampling.

Seriously, if you want 95% confidence than statistically you will need at least 30 shots. You will also find that what you think is a .5 MOA rifle and shooter combination with 10 shots will go up until you reach a 95% confidence interval. In the ballpark of >.75 MOA.

This is why we have a lot of data on this forum with people posting I have a single digit standard deviation one time like we'll say 8. Nobody ever comes back 500 or 1000 rounds later showing they are still achieving an SD of 8 with the exact same load.

We only use 10 shots with the chronograph because it is practical but random rather than statistically correct. It is a snapshot. Our starting point. But it is by far not the last word. I use this same method but I know it won't last. SD is important but it is by far not more important than small groups down range. We believe the bullet in the long run. Ever wonder why a chronograph calculates AVG, SD, and ES but doesn't spit out the confidence level. It is missing one important variable.

The OP's results are based on a couple of observations. He would need to do this over and over again though. It would be a waste of ammo and a barrel to try and prove his original observations are correct. It would be impossible to determine.
 
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#48
I’m not well edjumikated so this stats stuff is way over my head.

What I can say from my experience is if I get a decent SD/ES on ten shots and the load a above and below it closely show a similar pattern or even better minimal speed differences as well and I run with it I’ve yet to get burned by that load and I can comfortably load it without having to be within a kernel of powder or any other crap.

leap of faith based on a small observation?
Maybe,,,,but it’s working for me.
 
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#49
Steel head said:
I’m not well edjumikated so this stats stuff is way over my head.

What I can say from my experience is if I get a decent SD/ES on ten shots and the load a above and below it closely show a similar pattern or even better minimal speed differences as well and I run with it I’ve yet to get burned by that load and I can comfortably load it without having to be within a kernel of powder or any other crap.

leap of faith based on a small observation?
Maybe,,,,but it’s working for me.
Click to expand...

I think theres a lot of ways to get to the same or close to the same page. I try to tell myself that finding a good load isn't like figuring out rocket science. There are patterns, nodes, etc and I need to stop overthinking sometimes and try to find something thats consistent both at range and across the chrono. I use a cheap $100 chrono too, so I do take those numbers with a grain of salt.

Recently my load of TAC under 77gr TMK always had the best SD's and grouped the best... but at range didn't perform how I wanted it too. I also shot on two different days with 20* difference and at range POI and stringing increased/changed. Went back to the chrono and in my rifle, TAC was just too temperature unstable for me.

Idk... I just constantly tell myself to stop overthinking and pick something. I also try a lot of different things, and I do not shoot in legitimate comps, so I suppose I have more time to dick around
 
#50
Gustav7 said:
I think theres a lot of ways to get to the same or close to the same page. I try to tell myself that finding a good load isn't like figuring out rocket science. There are patterns, nodes, etc and I need to stop overthinking sometimes and try to find something thats consistent both at range and across the chrono. I use a cheap $100 chrono too, so I do take those numbers with a grain of salt.

Recently my load of TAC under 77gr TMK always had the best SD's and grouped the best... but at range didn't perform how I wanted it too. I also shot on two different days with 20* difference and at range POI and stringing increased/changed. Went back to the chrono and in my rifle, TAC was just too temperature unstable for me.

Idk... I just constantly tell myself to stop overthinking and pick something. I also try a lot of different things, and I do not shoot in legitimate comps, so I suppose I have more time to dick around
Click to expand...
I absolutely only started using chrony data for load development when I got my magnetospeed.
My older chrony was not trustworthy and I strictly observed vertical then.
 
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