Advice Needed: Statistical Samples from (Len,Wt) to measure MV

[CrimsonApostle]

Hi,

OK, a newbie on this forum… though I have done a lot of homework on long-range shooting. I need some statistical help on sampling. I had a college 300-level statistics class about 30 years ago, but I’m afraid that that is not helping out here! :'(

Here is the main issue: I am fairly new to long-range shooting. I bought a Savage Model 12 Long Range Precision in 6.5 Creedmoor with

• Sightron SIII 8-32x56 MOA-2 scope
• Ken Farrell base (30 MOA tapered)
• Ken Farrell scope rings
• Flatline Ops sight level
• Center Shot Rifles muzzle brake (had a local custom rifle guy thread the bore and set this all up right)

.
I have a very heavy rifle rest, and a very nice person at the 1000 yard range in Missoula took me to his house on the way home from a match, and made me a flat aluminum piece that screwed into the front of my rifle it can fit very snugly with the rifle rest. (I now know it is better to have the stock of the rifle have a completely flat and wide surface, but that is maybe for my next rifle …)

At a match late in 2013 in Missoula I had a group size of 21”. I think I can do a good deal better than that, but much of this is with your help. (BTW, one of the guys there just shot a 2.68” group in the light gun category, which is of course better than any heavy gun record. The record certification is pending: link). Finally, I should note that my son and I have had some long-range shooting classes.

I am an insanely busy technical professional so I don’t have any time to handload, at least not for at leat a few years. Ergo, upon the advice from some who owns the same rig as mine and who has shot on the US national team (lets call him “MM”), I ordered some semi-custom ammo. This company, which we’ll label “CC” (after the Unix C compiler), offered a load development service and then ammo based on it. I bought 1200 rounds from them and still have about 700 left. So I have to use them as best as I can. Ergo my questions to this forum. I paid for a load development service (~$250) then for the actual ammo (~$2.10/round). The rounds used a Berger Hybrid match with a G7 BC of .317 plus 8% that CC claimed from adding a point to the rounds.

Unfortunately, when I was at my local range last year, the CC ammo had a very big MV spread: at least 40fps (sample size of ~10; I know this is low) and there were not just one or two outliers. (I have to clean my garage to find my record book to get the exact numbers…) Very sad: I know from Litz’s book that this is pretty awful. And the chronometer seems to be very solid.

So I decided to do some measurements on the CC ammo, with a lot of homework ahead of time. Actually hired my 18-year-old son and his friend, both with very good math skills. (I have a BS in Math, but way too many years….) We measured length(in) and weight(g) of about 400 rounds. The idea here is that likely the MV depends on one or both of these. Originally some of the shooters at my 1000 yard range thought that this Berger bullet was heavily dependent on seating depth. But later they thought it was not dependent on seating depth. So maybe the MV depends only on the weight, which one presumes is dependent on the powder charge (brass and bullet weighing consistently). At least those are my novice suppositions.

Below is info on this. But my main point in posting to this forum is to ascertain which rounds I should use to test MV. Originally, the choice of my son and I was to choose an “almost-max” and “almost-min” in Len and Wt. “Almost” means not the outlier, but not far away whereby there are a lot of samples near it. So then we would have the cross product {almost-MIN, almost-MAX} X {almost-MIN,almost-MAX} for 4 sample sets. Probably I would be looking at 10-16 samples/set. The idea is to get the biggest cluster at each end of both variables. That should make it clear if the MV is dependent on one or both of those.

The other way of choosing a sample set is randomly. Methinks we should do as per above, with MAX an MIN, so to have a reasonable set for each combo of {MIN,MAX} (here “reasonable” includes the notion that this is high-quality match ammo, not garden-variety plinking stuff). But my son’s friend and now he think that we should do this random way. I have not had statistics as recently as my son and his friend have; but, of course, that does not mean that they have more common sense and/or wisdom on this issue. So inquiring minds want to know….
So whaddaya think? Below are some tables from my measurements. FWIW the length was calculated with a Hornady Electronic Caliper 6”, and for weight a Frankford Arsenal DS0750. Check out the reviews and specs there. Both were very repeatable.

But I need help in deciding how to choose the sample set from the CC cartridges. The local range I go to has a permanently-mounted Oehler 35P so we are probably pretty good here. I do know that when I brought a 300’ landscape steel measure it was within 1” from the end of the shooting bench to the middle of the target holder. So they seem to be very careful here. And even if it were set up not 100% über-perfect (e.g., the sensors a teeny bit too far away from each other) that would only affect the accuracy of the measurement, not its precision. I.e., the measured MV would have been spread out just as much.

To add more data into the mix, I also measured 20 rounds each from other 6.5 Creedmoor rounds:
1. Hornady Max 140-AMAX,
2. Nosler Ballistick Tip Trophy Grade 140BT, and
3. Nosler Custom Competition Match Grade 140 HPBT.

These were ones I could find at Midway (could not find any elsewhere). Besides measuring them now, I plan on firing a box of each of these to see the variance in MV for a full box and of course how, if any, it correlates with Weight and Length.

And, while this is not 6.5 Creedmoor, I bought my .308 hunting rifle and tried out some round. After a fouling shot the next 4 rounds with Federal Gold Medal 2343, {2524, 2523,2520,2550}. I know this is a small sample size, but this is a very very small STDEV. Kinda puts the 6.5 Creedmoor (a round supposedly only for competition) so shame.

So, then, here below are my data. Assuming that the seating depth does not matter on the 140 Berger Hybrid, the main issue here is the weight. I think… and welcome your input.

Summary Data
Here, “STD%” means the STDEV/MEAN. This normalizes the groupings, kinda, I think.

Sample Size Length STD% Weight STD%
CC Berger Hybrid Match 140 391 0.67064 0.44433
Hornady Max AMAX 140 20 0.1302 0.23629
Nosler Ballistic Tip Trophy Grade 140 BT 20 0.10878 0.19487
Nosler Custom Competition Match Grade 140 HPBT 20 0.16847 0.28146

Of course, the CC rounds were supposedly customized to the harmonics of my rifle (yes, I shipped it there). So, even though its STD% is greater, it may in theory perform much better than the STD% may indicate. Maybe. I’ll have a lot better data on that once I go to the range and measure MV with a well-chosen set of rounds. But, before I do, I need advice on how to take a sampling from my 391 CC cartridges. Please give me advice on how to choose well!

And, for that matter, I am wondering why someone getting factory match ammo would not go ahead and measure and/or weigh each round to try to group similar ones. At least if that made a difference with MV. Thoughts on this?

Finally, FWIW I have not yet measured another 300 or so rounds; I may well be able to do this before I go shoot. But the difference in the stats for 391 vs ~700 would presumably be minimal. And it does not affect the methodology by which I choose my sample rounds to shoot and measure MV.

Thanks in advance for any help here. I know that you guys are handloaders, but you are very well aware of all the variables that can affect MV in a round.

 

[stool]

way too much time with a pencil, too little time with the trigger.

 

[timeout]

I'm not on any shooting team, but IMHO all bullet/rifle combinations are dependent on seating depth and a whole bunch of other things. I hate to assume, so did the custom loader have your rifle in hand to develop the load? What did he give you for MV, SD and accuracy info? Another assumption, but I would assume that the person offering such a service is very knowlegdable and capable, ie his info provided to you should be accurate. I have a fairly good handle on the reloading process for accuracy. I feel like I could go a couple steps further yet BUT, I can see that my biggest long range shooting improvement will come from wind reading and applying that to actual scope or hold off changes. So long story short, I am guessing that you also will need to improve through trigger time. You could prove/disprove that theory to yourself by borrowing a little time behind the stock of a competitors rifle that is a known good shooter. Anyway, just my opinion and good luck with this endeavor!

 

[Elkbane]

Crimson,
If it were me, I'd take a different approach to your problem. I'd re-mearsure length to ogive with on your CC ammunition and breake them into quartiles.

Then I'd shoot a 10 round group from each quartile and see which ones group the best. Then I'd try to seat them all to the length that groups the best (hopefully the short ones shoot decent - it's easier to make them shorter than it is to make them longer). Measuring OAL on a VLD type bullet is fraught with measurement error because of the elongated shape of the bullet nose (I think you are seeing that in the data - compare VLD to non-VLD STD of length). Unless you measure them at the ogive (where it counts) you really don't have a useful measurement IMO.

Of course thisi would require that you purchase a press and set of dies.........calipers and ogive measurement tool........
Elkbane

 

[swampshooter]

I would test your sample from the extreme ends of your weight range. Shoot 2 five-shot groups, preferably at 100 yds. checking MV at the same time. Then I would weigh the loaded rounds and segregate them into .2 grain variation, or as close as you can. Then test them with 2 five-shot groups. Then further segregate the weight sorted rounds by ogive length. Because your rounds are already loaded this is probably the best that you can do. I would also check to see if Black Hills or Accuracy International or some other match grade ammo producer makes match grade ammo in your chambering and buy some for a comparison test.

 

[swampshooter]

I also think that if you were expecting your custom ammo to have single digit velocity spread and to shoot moa accuracy to 1,000 yds. that you should have specified this in the beginning. Development of match ammo with this degree of precision is very time consuming and would be very expensive if you had to hire someone else to do it.

 

[eric32]

i think what you need to find out what weather condition was the ammo developed and with what powder. You might be out of tune with the weather condition at your present location then that of where the ammo was developed and tested.

as mentioned already, if thats the case you might just have to seat the rounds deeper by .003 increments and hope you hit a better node.

 

[BoydAllen]

Do you know of anyone that has competed successfully at 1,000 yard benchrest using ammo that he purchased rather than loaded himself? I have not heard of anyone who has, but then I do not shoot that distance, or anywhere near it. Perhaps you need to sponsor a bright shooter that is not able to afford all of the costs of competition in exchange for his loading for you. Then you can follow the steps that the rest of the competitors do for working up and loading competitive ammunition, consulting with him throughout the process. To do this, you will probably need a very good electronic scale, and a case annealer, in addition to all the usual loading equipment.

 

[CrimsonApostle]

I hate to assume, so did the custom loader have your rifle in hand to develop the load? What did he give you for MV, SD and accuracy info?

He gave 2820 fps for MV, no SD info, but showed (and sent) me a 3-shot grouping (a tad under 0.5") as the only thing that might indicate anything remotely near SD. Yes, he had my rifle.

 

[CrimsonApostle]

I also think that if you were expecting your custom ammo to have single digit velocity spread and to shoot moa accuracy to 1,000 yds. that you should have specified this in the beginning. Development of match ammo with this degree of precision is very time consuming and would be very expensive if you had to hire someone else to do it.

Thanks VERY much for your comments here and in the other reply.

Nope, I don't have single-digit assumptions here from ammo that I or someone didn't load extremely carefully, or other such delusions of grandeur!

Its just that in his fantastic book, Accuracy and Precsiion for Long Range Shooting, Litz individually isolates the effects of different variables on both precision and accuracy. He very nicely then gives high confidence, medium confidence, and low confidence values for each (here low confidence means for a precision shooter, not for a good ole' boy plinking). For MV, the SDs were 10, 20, and 30 mph.

 

[BoydAllen]

For what you are doing, I have seen more than a few discussions that to me indicate that there are significant numbers of posters who have been blinded by their training in statistics, to the extent that they overlook an obvious fact. At least for the group part of long range shooting it is precisely the ES of velocity within each group that matters, including all outliers. To me all of this talk of SD for this application is just a waste of time.

 

[Buzz]

This may end up being one of those shortcuts that's not really shorter, and I really think you're just chasing your tail at this point. That ammo could very well have been sub .5 moa when it was developed, but changes in weather, altitude, throat erosion, etc. can have a great impact on accuracy. Sometimes barrels "speed up" after a few hundred rounds and the load needs to be tuned. If I develop a load in the winter when it's 50°, that load will usually need a little tweaking in the summer when it's 110°. If the load likes to be just touching the lands, the oal will have to be tuned every few hundred rounds. Now that you have 500 rounds down the barrel I'm not surprised you're having issues. You can tune what you have left in ammo, but I'd suspect that after another few hundred rounds and another change in season you'll be right back in the same spot you're in now.

I think what you've learned the hard way is that the loading process is just as important as actually shooting, and poor loads can take a lot of the fun out of shooting. I think you'll also find that load development and hand loading can actually be quite a bit of fun and adds to the shooting experience.

 

[stool]

a .5 inch 100 yd group does not work well at 1000 yds.
when i was building my 1000yd rifle i was told to build a rifle that would do 1/4 or less and then go practice.
lucky for me i got a bit less than that.
as others have noted money and statistics do not shoot rifles.
no one shoots factory nor purchased "custom" ammo in 1000yd br.( it appears i am wrong here)
you need to build and tune your ammo based on how it shoots...you need to do it.
someone suggested you sponsor a shooter, and have him load for you..might work, but few people have lots of free time.

I hate to assume, so did the custom loader have your rifle in hand to develop the load? What did he give you for MV, SD and accuracy info?

He gave 2820 fps for MV, no SD info, but showed (and sent) me a 3-shot grouping (a tad under 0.5") as the only thing that might indicate anything remotely near SD. Yes, he had my rifle.

 

[timeout]

CA has stated that he does not have the time to do his own reloading. While very informative, most of the reloading help given here is somewhat irrelevant. Someone can obviously build 1000 yard rounds for him by loading and testing with his rifle. Money can buy the reloading part, and the gun. No amount of money can replace trigger time. I doubt there are many consistently outstanding 1000 yard shooters that got there without putting a ton of time behind the trigger. Perhaps my assessment is wrong. Not the first time, won't be the last.

 

[CrimsonApostle]

a .5 inch group does not work well at 1000 yds.

Very sorry I was not clearer here ... but the half-inch group was at 100 yards, not 1000. Um, if it were at 1000 yards it would be only about 20% of the world record for a group of 10.

 

[CrimsonApostle]

CA has stated that he does not have the time to do his own reloading. While very informative, most of the reloading help given here is somewhat irrelevant. Someone can obviously build 1000 yard rounds for him by loading and testing with his rifle. Money can buy the reloading part, and the gun. No amount of money can replace trigger time. I doubt there are many consistently outstanding 1000 yard shooters that got there without putting a ton of time behind the trigger. Perhaps my assessment is wrong. Not the first time, won't be the last.

Very good advice here, timeout! I'm not concerned about being consistently "outstanding" at 1000 yards, just trying to get better. And, besides reading the wind, SD of MD is something that can matter a lot and which I can presumably do something about.

Would it be tacky to also post this to the competition forum? If not tacky, it may well not be productive, but one never knows. I have been very impressed with the numbers of replies so far.

I do need more trigger time! A range that goes to 500 yards (but with no wind flags) is an hour's drive away. The Missoula range is a 5 hour drive.

Longer term I am working on the problem .... I live in a rural college town, and in a few years I hope to move out to the countryside. I can find somewhere with a 1000 yard shot with backstop if I look hard enough. I would have it heavily instrumented for wind, remote camera for seeing where things hit, etc (I'm a professor in a technical area). But that is a few years at least in the future. For now, I am just trying to learn what I can about the whole space and get better. And if I can move to the countryside then I can do a lot of shooting. But this time learning and doing what I could would be very very helpful. We'll see if I can pull it off!

 

[CrimsonApostle]

OK, here’s an update. We went and weighed and measured almost all the rounds … ran out of boxes. But we’re at almost 800 now. Here’s an update and a few more questions and comments to some of the replies.

My son thinks using a random selection better than testing extremes, and others on this forum agree. He told me about how the square of the sample size affects the SD of the mean (not of the samples, but of the mean of a given sample compared to of all samples).

Still, I don’t really know how many rounds I should go and measure the MV of, and he did not know either. I don’t have a clue where the law of diminishing returns kicks in for my purposes and gear here. I have 540 rounds left of CC, 180 of Hornady AMAX 140, 80 of Nosler Match Grade 140, 20d of Nosler Trophy Grade 140. I am going to take a pragmatic guesstimate here and shoot 40 of CC and 20 of the others. Any advice if this is enough? (Even if its overkill, I think I won’t go below 40 for the CC just to be extra certain.)

Here are some replies to some comments folks have given...

• I can’t measure any ogive or anything other than the overall length and weight.
• Black Hills and Accuracy International unfortunately don’t make 6.5 Creedmoor ammo (very good suggestion though).
• I am well aware that no 1000 yard shooter is competitive with factory gear and factory or semi-custom ammo. I am just trying to compete against myself and become a much better shooter. Eventually I’ll likely get better gear and get very serious about reloading, but I have a lot I can learn in the mean time. Indeed, what I learn may well inform my choices in a custom rifle, reloading strategies, etc.
• 
  I do know that the weather conditions when the ammo was made was will affect the ballistics. For a sniper who is trying for a one-shot kill that could be crucial. But I don’t see how that will affect me in a 1000 yard competition. The day before I go and make sure that its close. Then I get 10 minutes of sighter rounds (only need about 5-10) where each hit is marked with a big visible plastic thing. So I get to adjust my scope to the weather conditions that day. How would knowing the weather conditions under which it was manufactured help here?

Thanks very much for the replies to date, and thanks in advance for any replies to these followup questions.

 

[eric32]

If the powder charge was tested at a given temp it will result in X FPS for that given load. Tempature will affect powder burn rate thus if it's colder slower muzzle velocity hotter faster muzzle velocity. Thus throwing your rifle out of a possible accuracy node

 

[Erik Cortina]

I tried to read all the posts but got tired.

So, you are trying to be competitive with a factory Savage rifle, with preloaded ammo that shot a .5" three shot group at 100 yards? Sorry, it does not work that way.

Here is what you need to do if you want to be competitive.
Find a great gunsmith and have him build you a full custom rifle.
Pay someone to teach you how to hand load match winning ammo.
Buy the equipment and tools necessary to load great ammo.
Work up a load, tune your gun, and go compete.

You are wasting time trying to be competitive with the combination you have now. Instead of troubleshooting problems, you would be better off loading consistent ammo for a very high performing custom rifle. "There are no short cuts to any place worth going!"

 

[Webster]

You don't have time to reload or go to the range but you want to be successful at long range. Won't happen no matter what your statistics tell you. Bench technique, gun handling and understanding wind conditions, temperature and other things can only be learned by shooting or mentoring. If your trying to teach yourself it's very difficult.