Question on SD. How many shot per group is sufficient?

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luckey

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Hi, a newbie question for the long range guru here. I am working on a load for 1000-yard steel match and wonder how many shot per group is sufficient to get a trustworthy SD and in what range the SD is accurate enough for this application? Thanks!
 
The answer depends on how much of a perfectionist you are.

Keep in mind that your velocity will change according to factors that may not be directly related to your load such as how fouled your barrel is, temperature of the atmosphere, temperature of your ammo, temperature of the barrel and chamber and even how long the round resided in your chamber prior to firing. (consider thermal expansion and thermal transfer)

If you are going to build a record of data, then you really might want to associate such factors that way you can estimate where on the range of variance the conditions correlate and have ballistic data available during the match to reflect and anticipate that.

Or just use the WAG method and know that on a cold day your ammo is slow and aim a little high and the opposite on a hot day. This will lead you to the next logical question... how high on a cold day? Well now you're right back to the beginning of this post.
 
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By steel match do you mean you simply need an impact off a built positions under a timed deal or is it a comp in which you are prone or at a bench and are going for group size ??
 
luckey said:
Hi, a newbie question for the long range guru here. I am working on a load for 1000-yard steel match and wonder how many shot per group is sufficient to get a trustworthy SD and in what range the SD is accurate enough for this application? Thanks!
Click to expand...

How far can you shoot on paper right now?

This question REALLY matters.

Jerry
 
Thanks everyone for input and questions. I thought I put enough backgorund, guess not. :) so please allow me to try again
1. Match accuracy requirement. 1 point for 1 impact on steel, no grouping requirement for the same target as you will move on to next one upon impact the first. 90 sec limit per stage.
2. Current skill level. With my own handload, at my range, the longest Range is 200 yard. I can shoot 0.5 to 1 moa. Never try beyond that. Surplus is 1-2moa(hirtenberger). That's on the bench, bipod front, rear on shoulder, no rear bag. My dial and hold over are both accurate, but never clock myself with a timer.

Yesterday at range to verify my final recipe, for 5-shot group, best SD 3.x, average 7-8. 10-shot group about 11, 20-shot 15-16. That should be ok?
 
What did the target show you?

What is the average group size? what is consistent? What is the vertical dispersion like?

That is what matters. It becomes very difficult when you cannot test at further distances to really know what is happening to your bullets. I fully understand that for many, a chronie is the only window they have into LR performance. The problem is that it is far from perfect a system and small changes in powder charge can have massive changes in LR tuning.

Why we try and tune at the furthest distances we can. many times, the best LR loads also have very good SR numbers and groups BUT all too often, SR numbers don't play out at LR so there really is no way to know. Sometimes groups that don't look all that wonderful at 250yds, become the best option at 1000yds

From 250yds, I will confirm at 800m to 1000yds and beyond.... or as far as the application demands.

Jerry
 
Not an expert or an F-classer like Jerry but do OK at the PRS type matches I run (although I don't really count).

I go for a single digit SD and a minimum sample size of 10.
 
guess I will find out soon. the only chance I can shoot beyond 300 is @ the match which is less than a month from now. ;)
 
I should add that I do my load development at 100 and then do validation at further distances.

I have never seen the "shoots poorly at 100 but gets better at distance" thing but I did have loads with good SD/ES numbers that did not shoot so there is always the need to check.
 
luckey said:
guess I will find out soon. the only chance I can shoot beyond 300 is @ the match which is less than a month from now. ;)
Click to expand...

There have been times when weather has stopped me from testing further. What I focus on is consistency in the grouping and most important the vertical dispersion.

At 200yds, you should be able to see variations of 0.1gr on your target wrt to vertical tuning. You should be as low as possible. 1/4 to 1/3 min tall should be achieveable with good brass prep and scales. The windage may be 1/2 min to 2/3 min but the bullets will land in a flat pattern. Looks like a football on its side... ideally, a line across the target center 2 bullets tall.

Then repeat that load and 0.1gr +/- over several range trips. Compare to the chronie data and pick the one with the best of all that you can test.

elevated pressures will not help you here. In all cartridges, there is a low, mid and high node before pressure signs becomes obvious. Most talk about the high node cause it sounds great on paper.... higher velocity should be less drift... better scores. Would work if you could keep the load in tune under match conditions. All too often, these loads are on a razor's edge and any change in effective load tuning and you have a train wreck. Typically, it looks like you can't find the center of the target as you go above and below at distance. I call this ping pong.... hit high, aim low, hit low, aim center, go somewhere else.

The windage may not look all that bad but the vertical can expand to 2MOA or more... the odds of hitting the target, not good. We get a bunch of PRS shooters while we are shooting F class matches in Washington. All the common chamberings and bullets, with all the common tuning problems. At 1000yds, you can see them chase their impacts all over that target - high and low. I am sure all have had very good SR tuning with great SD/ES... didn't mean a hill of beans on target.

Many top F class shooters have discovered that the mid node is where the good stuff lives. The nodes are typically wide, stable and behave themself over a wide range of temps. How about test at -5C in the winter... go to Arizona and set an NRA score record in 28C at 1000yds

Assume you are shooting the 308? there will be plenty of info on how to hot rod this chambering... I am far down this rabbit hole and have plenty of crappy relays to tell you, doesn't work. If you can't test and confirm at LR, I would suggest you work around book loads and velocities. Sure, you could get another 75fps with XYZ super duper load... if you can't confirm that tuning at distance, that 75fps will be the most frustrating "gain" you will have.

Currently shooting lots of 6.5 CM at LR and have helped a local shooter get going. he can only test at 440yds but that was plenty far enough to find that the mid node behaved the best (which is almost a 'max' print load). Cold bore at 975yds was almost a hit... just down wind. He had lots of hits all the way out to 1445yds. Vertical was almost non existant so I was able to center his group wrt to the winds and he was hitting SUB MOA targets. he did bring down some "better" loads which totally fell apart at distance. Quite eye opening when a super zapper load has 4 FT of vertical dispersion at distance....makes it real hard to hit milk jug size targets.

His best loads were around 6" vertical at 1445yds..... and he was putting hits on an 8 inch rock face. His magnetospeed suggests he is right at 2600fps which is slow... so what?

You can see pics and info on my facebook page... mystic precision inc.

If you can't confirm at distance, be conservative at SR... load towards the max loads in printed data and tune for the lowest vertical possible. It will drift more at distance BUT you can adjust for that because the next shot will follow your direction.

And that is how you put hits on target.

Jerry
 
Hi Jerry.

Thanks for all the sound advices. That was what I have been doing. Just an update. My last trip has confirmed my load to the best I could given the range limit(200 yards). What I did was to zero the rife @ one range @ 100 meters, 5-shot groups(tested 3) were all touching each other. then moved to another 200-yard range, tested same 5-shot group @ 100 yards and 200 yards. @100 yard, same accuracy, @200 yards, around half MOA, definitely within 1moa. I know the group opened up mostly because of my skill, not the load as all the 5-shot SDs were less than 10, as little as 0.9. 10-shot SD was at 10, 11. So, this should be the load I am looking for. the next test, to verify all data, I think I will dial all the way up to 1000 yards, and then hold back down to 100 and 200 yards, it's not the same as shooting long range, but at least further confirm the ballistic data. Then I have to see how I would do on the match day with the wind and my own hands. :)

Thanks again for everyone's great input and good advices. I have learned so much over the years on CGN!


Mystic Precision said:
There have been times when weather has stopped me from testing further. What I focus on is consistency in the grouping and most important the vertical dispersion.

At 200yds, you should be able to see variations of 0.1gr on your target wrt to vertical tuning. You should be as low as possible. 1/4 to 1/3 min tall should be achieveable with good brass prep and scales. The windage may be 1/2 min to 2/3 min but the bullets will land in a flat pattern. Looks like a football on its side... ideally, a line across the target center 2 bullets tall.

Then repeat that load and 0.1gr +/- over several range trips. Compare to the chronie data and pick the one with the best of all that you can test.

elevated pressures will not help you here. In all cartridges, there is a low, mid and high node before pressure signs becomes obvious. Most talk about the high node cause it sounds great on paper.... higher velocity should be less drift... better scores. Would work if you could keep the load in tune under match conditions. All too often, these loads are on a razor's edge and any change in effective load tuning and you have a train wreck. Typically, it looks like you can't find the center of the target as you go above and below at distance. I call this ping pong.... hit high, aim low, hit low, aim center, go somewhere else.

The windage may not look all that bad but the vertical can expand to 2MOA or more... the odds of hitting the target, not good. We get a bunch of PRS shooters while we are shooting F class matches in Washington. All the common chamberings and bullets, with all the common tuning problems. At 1000yds, you can see them chase their impacts all over that target - high and low. I am sure all have had very good SR tuning with great SD/ES... didn't mean a hill of beans on target.

Many top F class shooters have discovered that the mid node is where the good stuff lives. The nodes are typically wide, stable and behave themself over a wide range of temps. How about test at -5C in the winter... go to Arizona and set an NRA score record in 28C at 1000yds

Assume you are shooting the 308? there will be plenty of info on how to hot rod this chambering... I am far down this rabbit hole and have plenty of crappy relays to tell you, doesn't work. If you can't test and confirm at LR, I would suggest you work around book loads and velocities. Sure, you could get another 75fps with XYZ super duper load... if you can't confirm that tuning at distance, that 75fps will be the most frustrating "gain" you will have.

Currently shooting lots of 6.5 CM at LR and have helped a local shooter get going. he can only test at 440yds but that was plenty far enough to find that the mid node behaved the best (which is almost a 'max' print load). Cold bore at 975yds was almost a hit... just down wind. He had lots of hits all the way out to 1445yds. Vertical was almost non existant so I was able to center his group wrt to the winds and he was hitting SUB MOA targets. he did bring down some "better" loads which totally fell apart at distance. Quite eye opening when a super zapper load has 4 FT of vertical dispersion at distance....makes it real hard to hit milk jug size targets.

His best loads were around 6" vertical at 1445yds..... and he was putting hits on an 8 inch rock face. His magnetospeed suggests he is right at 2600fps which is slow... so what?

You can see pics and info on my facebook page... mystic precision inc.

If you can't confirm at distance, be conservative at SR... load towards the max loads in printed data and tune for the lowest vertical possible. It will drift more at distance BUT you can adjust for that because the next shot will follow your direction.

And that is how you put hits on target.

Jerry
Click to expand...
 
Well said Jerry. There is no substitute for holes in paper at long range. I see lots of shooter, especially in the PRS crowd, you do their load development with a chrony at 100m. Sure, you might have an ES in the single digits, but you don't know how your barrel is moving.
 
I think this topic is very interesting and we all know that there are about a million different ways to do load development - according to the internet at least.

I use a chrony at my 100M range as a starting point for my load development. I look for a load that shoots well (I pick something in the .5" range and don't care to try much harder as it doesn't make a difference to me) and has a good ES/SD. I fully agree with what other have stated - a good ES/SD does not equal a good load (when I did my 6.5X47 development I had a load that had a ES of 5 but the groups were ~0.75" on average).

However, I disagree with the statement that a good LR load can have a large ES/SD. Lets say that you have a SD of 15 (not really that bad but not great). This means that 68% of your are within 1 SD (in this case 15 FPS) of your average. This is a spread of 30FPS and that equates to over 12" difference at 1,000M.

I think to have a good load you need to look at what the paper is telling you and intelligently use the Chrony.

Personally, if I had a group that shot in the .1s at 100 but had a big ES/SD I would not try to see what that load did at distance because logically (to me at least) big FPS spreads will cause vertical at distance.
 
If your load at 100yds/m is one hole and it opens up to 1/2 MOA at 200yds/M, you have a BAD load. When prepping for the Worlds 2013, I cooked up a load that put 18 of 19 rds into 1/8" group at 100yds... this load couldn't stay on a piece of paper at 600m.

Trust the target, tune at 200yds for the smallest group with the flattest vertical. It can be 1 hole tall at 200yds.. YES, a line of bullets across the target. This is where you see the benefit of investing in quality milligram scales, proper reloading tech, and good barrels.

If you can launch bullets into 1 hole at 100yds, you have the skill to shoot very well AND the delivery at longer distances shouldn't change. If the load doesn't work at longer distance, either spend more time practising or fix your rifle/load. DON'T MAKE EXCUSES FOR THE AMMO/RIFLE.

Youtube is littered with reviews where they will immediately discount a wide shot as a "pulled" shot when looking at the target. If it was pulled, it should be called BEFORE going to the target and the direction of the pull should be noted.. not at the target to make the system look better. This is why many novice go to competitions and wonder why their wonder rig shoots like absolute garbage at distance. Successful competitors do not discount flyers... we count EVERY shot and if we made a bad pull, that shot better go where we say we pulled it. If it doesn't, better start look at the gear and ammo.... or spend more time learning how to shoot.

I don't think you have discussed what type of chronie you are using. The basic red box and any other entry level chronie have a built in error of 1/2% MINIMUM. That is baked into the machine.

So a 3000fps reading is +/- 15FPS when it is working PERFECTLY. An ES of 30 is hard wired into the machine at this velocity. If the light varies, this can cause more error.

Some of the best chronies bring this down to 5fps... you can confirm the specs on the Oehler 35.. and new 2 chronie set up. What I am simply saying is the error of the machine may be higher then the numbers you are trying to crunch. Saying you have an ES of 10 when your machine can't do better then 30 is just fooling yourself.

And this is why I suggest you use the chronie to get a velocity reference for your drop table and the target to determine the tune.

YMMV

Jerry
 
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No.... I stopped using a chronie all the time when I found it didn't matter at distance. I find the load THEN I get the speed for my drop chart.

I have seen SD/ES numbers that would not have been impressive hammer at 1000yds. For the most part, good 1000yds loads have very good numbers BUT good numbers doesn't mean it will shoot well at LR.

Do some research on positive compensation.... at the end of the day, that is what we are trying to tune for.

Jerry
 
Hi Jerry, just to clarify, when I said "100yd/meter holes are touching", it was still half moa, but more concentrated than @200 yard where I got 0.5moa-1moa, but the holes were not as dense as I liked. I am quite sure that it was me because I wasn't very consistent that day in a few ways, which is another matter outside of this post.

My chrono is labradar which is pretty good as far as I can tell. And for my load, I have to admit that I am a control freak. My brass is absolutely shiny, primer hole is completely cleaned and uniformed, then, I use two scales(one electric, one beam) to cross check and accurate to one kernel(about 0.02gr/kernel), seat the bullet with competition die with micrometer(no runout at all), and last but not least, two light crimps with ammo turned 90 degrees. So, my production rate is very low, about 25 rounds per hour(powder/seating/crimp), but I trust the quality of the load which did show on the range(up to 200 yards of course).

to get to this load, I went through 37 recipes, with combination of 0.2gr increment, 0.01" Ogive change and 3 different primers(BR-2, 210 and 210M). the data I collected matched up my targets so far. after all, it's short distance.

Mystic Precision said:
If your load at 100yds/m is one hole and it opens up to 1/2 MOA at 200yds/M, you have a BAD load. When prepping for the Worlds 2103, I cooked up a load that put 18 of 19 rds into 1/8" group at 100yds... this load couldn't stay on a piece of paper at 600m.

Trust the target, tune at 200yds for the smallest group with the flattest vertical. It can be 1 hole tall at 200yds.. YES, a line of bullets across the target. This is where you see the benefit of investing in quality milligram scales, proper reloading tech, and good barrels.

If you can launch bullets into 1 hole at 100yds, you have the skill to shoot very well AND the delivery at longer distances shouldn't change. If the load doesn't work at longer distance, either spend more time practising or fix your rifle/load. DON'T MAKE EXCUSES FOR THE AMMO/RIFLE.

Youtube is littered with reviews where they will immediately discount a wide shot as a "pulled" shot when looking at the target. If it was pulled, it should be called BEFORE going to the target and the direction of the pull should be noted.. not at the target to make the system look better. This is why many novice go to competitions and wonder why their wonder rig shoots like absolute garbage at distance. Successful competitors do not discount flyers... we count EVERY shot and if we made a bad pull, that shot better go where we say we pulled it. If it doesn't, better start look at the gear and ammo.... or spend more time learning how to shoot.

I don't think you have discussed what type of chronie you are using. The basic red box and any other entry level chronie have a built in error of 1/2% MINIMUM. That is baked into the machine.

So a 3000fps reading is +/- 15FPS when it is working PERFECTLY. A SD of 30 is hard wired into the machine at this velocity. If the light varies, this can cause more error.

Some of the best chronies bring this down to 5fps... you can confirm the specs on the Oehler 35.. and new 2 chronie set up. What I am simply saying is the error of the machine may be higher then the numbers you are trying to crunch. Saying you have an SD of 10 when your machine can't do better then 30 is just fooling your self.

And this is why I suggest you use the chronie to get a velocity reference for your drop table and the target to determine the tune.

YMMV

Jerry
Click to expand...
 
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Mystic Precision said:
No.... I stopped using a chronie all the time when I found it didn't matter at distance. I find the load THEN I get the speed for my drop chart.
I have seen SD/ES numbers that would not have been impressive hammer at 1000yds. For the most part, good 1000yds loads have very good numbers BUT good numbers doesn't mean it will shoot well at LR.
Jerry
Click to expand...

The problem with any type of chronograph is the accuracy level may be less than the true velocity spread. In that case you are no longer measuring your bullet speed but actually the accuracy of the chronograph.

I still think it's good to have a Labradar next to you when possible just for the sanity check. When a round goes low you can compare that to the velocity and help identify if it was a slow round or a condition you missed.

David Tubbs uses a Magnetospeed that is mounted on a rod that is mounted to his forend, so it does not mess with his barrel harmonics. (Great idea BTW) And he uses this for shooting I think around 1.5 to 2 miles if I'm not mistaken.

So feedback does have value, as long as you accept it with a grain of salt and with realistic expectations. Without it, you can only suppose and theorize with less than all the supporting data.... flawed or not.
 
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