A Standard Deviation Primer with Picture
- Thread starter markr6754
- Start date
whatever."Guys...this post wasn't made to piss anyone off. I got new bullets, I had never used them before. I was curious how close they came to 115gr and started weighing them. As I've never weighed out a box of bullets before I was surprised at the rather extreme (to me) spreads, but also noticed that this was "Normally Distributed" data, and thought it would be a good use to determine the sd, mean, mode, and etc. Now, I had been challenged in another thread about my use of sd, so of course I thought I'd share what I'd already been working on since last Friday.
It wasn't my intent to throw my credentials in anyone's face...I responded to a specific questions from 74A95.
Clearly I made some angry, pleased others, and came off looking like an a$$...I do apologize. As a new reloader I thought I had something helpful to share...but I missed the mark.
I'd like to apologize openly to higgite, buck460xvr, Metal God, Jim Watson, Ruga Booga, Aguila Blanca, and anyone else that I antagonized. Really, I'm not an a$$, though I may have come off like one. You guys have all provided value to me since I came to this site in February, along with many others. Thanks for your patience, and pardon...should you offer it.
It wasn't my intent to throw my credentials in anyone's face...I responded to a specific questions from 74A95.
Clearly I made some angry, pleased others, and came off looking like an a$$...I do apologize. As a new reloader I thought I had something helpful to share...but I missed the mark.
I'd like to apologize openly to higgite, buck460xvr, Metal God, Jim Watson, Ruga Booga, Aguila Blanca, and anyone else that I antagonized. Really, I'm not an a$$, though I may have come off like one. You guys have all provided value to me since I came to this site in February, along with many others. Thanks for your patience, and pardon...should you offer it.
I don't see where the OP did anything to apologize for, this thread sure beats the unsolvable "help me I have fallen and can't reach my bench" threads.
Only thing I would criticize here this is what I criticize on most weighing thread is if you are not using a scale that is capable of .0001 grams you are spinning your wheels. If your measurements were done on a typical .1 gn scale the readings are subject to a = or - .1 error.
Only thing I would criticize here this is what I criticize on most weighing thread is if you are not using a scale that is capable of .0001 grams you are spinning your wheels. If your measurements were done on a typical .1 gn scale the readings are subject to a = or - .1 error.
Thanks for the apology but that is not necessary , really . It takes quite a bit to upset me and the mods on here tend to stop any dialog way before anyone gets me mad . My point in this thread and the other was simply . When talking SD in relation to firearms velocity , it's not just a straight numbers game . As I pointed out earlier , just how you hold the firearm can effect those numbers . There are many variables that effect velocities and there consistency . This is why I saw nothing in your bullet example that really related to the other thread . Your bullet weight SD sheet was really only dependent on the quality of your scale as the number one variable . Everything else is fixed and can't be changed . While internal/external ballistics are dependent on the constancy of the charge , primer seating , bullet , neck tension , firearm hold etc etc etc . Which is all dependent on a human 
This is why in firearms the SD IMO is best described as what the likely difference will be from one shot to the next . Although your bullet graph is interesting It does not really tell me what the likelihood one bullet will weigh compared to the next with out doing more math , therefore not that helpful to me . You did bring up this was so we could understand SD as it relates to the other thread or at least that's how I read that . I'm no math beautician but in my head your bullet chart does not help me understand velocity SD's . I'm open for some learning if you can help explain how it relates ?? or anyone else for that matter ?
Regardless let me thank you for even doing that bullet test . I do my fare share of testing and posting of results on this and other forums . Sometimes I feel people don't get the time involved to do some of the testing and then post the results . Be sure that I at least understand the effort you made and appreciate it none the less .
This is why in firearms the SD IMO is best described as what the likely difference will be from one shot to the next . Although your bullet graph is interesting It does not really tell me what the likelihood one bullet will weigh compared to the next with out doing more math , therefore not that helpful to me . You did bring up this was so we could understand SD as it relates to the other thread or at least that's how I read that . I'm no math beautician but in my head your bullet chart does not help me understand velocity SD's . I'm open for some learning if you can help explain how it relates ?? or anyone else for that matter ?
Regardless let me thank you for even doing that bullet test . I do my fare share of testing and posting of results on this and other forums . Sometimes I feel people don't get the time involved to do some of the testing and then post the results . Be sure that I at least understand the effort you made and appreciate it none the less .
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Gary Wells
New member
Mark:
That SPC chart probably would have looked much better had the numbers been fed into a SPC program which would have set the chart not as every thou tenth but something that would not have displayed the missing numbers slots. Very interesting chat though. I've plotted quite a few boxes of loaded rounds, both factory & homegrown, empty cases & projectiles & my charts came out very similar to yours (missing slots).
That SPC chart probably would have looked much better had the numbers been fed into a SPC program which would have set the chart not as every thou tenth but something that would not have displayed the missing numbers slots. Very interesting chat though. I've plotted quite a few boxes of loaded rounds, both factory & homegrown, empty cases & projectiles & my charts came out very similar to yours (missing slots).
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If you really want to have fun with statistics, shoot a shotgun at a patterning board and then plot the x and y axis positions of the hits and see if you don't come up with a two dimensional bell curve.
When you shoot a rifle at a target hundreds of times, the hits should look like a very tight shotgun pattern and should form a two dimensional bell curve. The more accurate the rifle, the sharper the peak.
When you shoot a rifle at a target hundreds of times, the hits should look like a very tight shotgun pattern and should form a two dimensional bell curve. The more accurate the rifle, the sharper the peak.
Nothing to apologize for.
When we load ammo, we work for consistency. Bullet weight is simply one of those variables. Powder weight, powder volume, case volume, case length, primer quality, COL, etc. We control the variables we can control. There are plenty of other variables we are NOT able to control. As a result, velocities right out of the barrel tend to be inconsistent in spite of our best efforts to control everything else. With inconsistent velocities, we have other inconsistencies beyond our control.
It's overwhelming, to be sure. If you can, create charts for everything else we try to do when loading. See how that works when you get to the range. (I expect it will work quite well, actually.)
If we reduce loading to a math problem, the variances might make it too overwhelming to even give it a try. Nevertheless, when we're hunting or shooting holes in paper, we really do quite well, all things considered.
I like your chart out of curiosity, however, it doesn't exactly solve all of the issues we have when loading and shooting. It's a prime example of how a paper problem may not exactly translate to a real life solution.
Carry on. It's a good way to think about it.
--Wag--
When we load ammo, we work for consistency. Bullet weight is simply one of those variables. Powder weight, powder volume, case volume, case length, primer quality, COL, etc. We control the variables we can control. There are plenty of other variables we are NOT able to control. As a result, velocities right out of the barrel tend to be inconsistent in spite of our best efforts to control everything else. With inconsistent velocities, we have other inconsistencies beyond our control.
It's overwhelming, to be sure. If you can, create charts for everything else we try to do when loading. See how that works when you get to the range. (I expect it will work quite well, actually.)
If we reduce loading to a math problem, the variances might make it too overwhelming to even give it a try. Nevertheless, when we're hunting or shooting holes in paper, we really do quite well, all things considered.
I like your chart out of curiosity, however, it doesn't exactly solve all of the issues we have when loading and shooting. It's a prime example of how a paper problem may not exactly translate to a real life solution.
Carry on. It's a good way to think about it.
--Wag--
buck460XVR
New member
Like others here, I need no apology. I'm rather old school, where my Daddy taught me well and my Momma raised me right. This meant that I was taught that modesty is a virtue and Pride is the worst of the 7 deadly sins. Kinda why I dislike Facebook and why I tend to detest braggarts. I realize that you are excited about your new hobby and you want to pass along any help you can.
This post tells me one thing for sure...don't buy Everglades bullets.
But in reality, it is the stacking of the variables that affects reloaded ammo the most. One set can have some variation and you can still get acceptable groups, especially if you are in a node. But take the heavy bullet with the low powder charge and weak ignition in the higher case volume compared to the light bullet with the high powder charge and strong ignition in the smaller case volume and you have a higher chance of having a higher Extreme spread.
What would actually be valuable is knowing what bullet weights and case weights can be discarded and which can be used (variables we can measure pre-assembly) to keep the SD within single digits. When I load for my precision rifles, that is something I look at. For pistol rounds, I just buy bullets that don't have a large variation like the OPs sample.
But in reality, it is the stacking of the variables that affects reloaded ammo the most. One set can have some variation and you can still get acceptable groups, especially if you are in a node. But take the heavy bullet with the low powder charge and weak ignition in the higher case volume compared to the light bullet with the high powder charge and strong ignition in the smaller case volume and you have a higher chance of having a higher Extreme spread.
What would actually be valuable is knowing what bullet weights and case weights can be discarded and which can be used (variables we can measure pre-assembly) to keep the SD within single digits. When I load for my precision rifles, that is something I look at. For pistol rounds, I just buy bullets that don't have a large variation like the OPs sample.
condor bravo
New member
I might also ask what the point is for the SD post. For a more practical answer, I would suggest that the OP divide the bullets into three groups, the lightest third, the middle third, and the heavist, load them all the same, and bench rest a sample from each group at some nominal distance, to determine if the results show any real difference in group size and point of impact. If so, the post could be more meaningful, but one such sampling may not prove anything due to factors other than .2 gr extreme spread entering the exercise.
Jim Watson
New member
I did that one time, light, middle, and heavy, plus random.
The random draw out of the box shot the most accurately from Ransom Rest.
I quit worrying about bullet variation at pistol ranges.
The random draw out of the box shot the most accurately from Ransom Rest.
I quit worrying about bullet variation at pistol ranges.
My initial thought was the same...except that the price was better than anything else I’ve encountered, $0.0625 per bullet. These bullets “look” really good...as if that is any kind of proof of quality. If I elect to exclude any bullets that fall outside of 1sd, the result comes to $0.096 per bullet. Still pretty decent. Several mentioned separating the bullets into several ranges...which I did, but actually used more than 3 ranges. Reality says that I will load and shoot all of these bullets, as this was an academic exercise.
So I decided to do more research...are these outlier bullets acceptable? When does a bullet become unacceptable?
I downloaded the SAAMI spec manual to find the answer.
As it turns out...Everglades Ammo advertising was spot on...these are truly SAAMI spec bullets. For 100gr and heavier lead core bullets, nominal weight +/- 1.5% is acceptable. For 115gr bullets, this means 113.275 to 116.725gr will pass the test.
https://saami.org/wp-content/uploads/2018/01/Z299-3_ANSI-SAAMI_CFPandR.pdf
Page 73 (82), of the document.
Gary Wells
New member
mark6754:
Are you open to suggestions? I liked your thread and the info that it contained. I hope that you will continue to post up data like that. Regardless of the neessity, there's always somebody looking for that data, maybe not today, but tomorrow. You might want to look up JayhawkNave02 over on 1911Forum & Bullseye-l-Forum. He puts up his charts on Excel.
Are you open to suggestions? I liked your thread and the info that it contained. I hope that you will continue to post up data like that. Regardless of the neessity, there's always somebody looking for that data, maybe not today, but tomorrow. You might want to look up JayhawkNave02 over on 1911Forum & Bullseye-l-Forum. He puts up his charts on Excel.
I suspect the SAAMI specs are their specs for testing chamber pressure in controlled lab conditions, and those specs are absolutely meaningless to the rest of the people on the planet.
In my plinking handgun loads , I don't think I'd be happy with that spread but at the same time not sure I'd care either .
Interesting you guys are talking about Everglades bullets . I just came across there website a few months ago and bought 2k of there 158gr 38/357 JHP bullets . They're HP but also SP as well , they are more like a semi jacketed HP with the top 1/3 to 1/4 of the bullet being exposed lead . They came a little dinged up on the edges of the tip but when I seat them my seating stem smashes all the burrs down and they end up looking pretty good loaded .
They came in 250ct bags . I'll have to weigh all the bullets in one bag and see what kind of variance I get .
I see similar results with cast handgun bullets, but not with higher end plated pistol or any rifle (mostly buy Sierra and Berger). Could care less about the differences on the handgun side and I suspect the manufactures feel the same way since what you found is not uncommon.
Something to chew on...
Small changes in weight does not translate to differences in BC unless you are passing certain velocities (velocity barriers vary by bullet).
Where the extra material is may or may not change pressure. Fatter may (tight), below the ogive may (less volume), above the ogive won't unless you are not seating by measuring ogive else it may because you are changing volume.
Pressure differences from volume or neck tension will impact accuracy long before small variations in bullet weight, as will variances in powder charge (that +/-0.1 is a big deal) at 100 - 200 meters, and 1 kernel is a big deal above 500 meters.
If you load rifle and you find your ogive measurement varies from one round to the next, it is most likely attributed to differences in neck tension from one piece of brass to the next. Microscopic burrs around the mouth, inconsistent annealing, and carbon build up (or lack of any carbon) are common reasons for different neck tension.
Point is, far more things are going to mess up your game before small changes in bullet weight.
Something to chew on...
Small changes in weight does not translate to differences in BC unless you are passing certain velocities (velocity barriers vary by bullet).
Where the extra material is may or may not change pressure. Fatter may (tight), below the ogive may (less volume), above the ogive won't unless you are not seating by measuring ogive else it may because you are changing volume.
Pressure differences from volume or neck tension will impact accuracy long before small variations in bullet weight, as will variances in powder charge (that +/-0.1 is a big deal) at 100 - 200 meters, and 1 kernel is a big deal above 500 meters.
If you load rifle and you find your ogive measurement varies from one round to the next, it is most likely attributed to differences in neck tension from one piece of brass to the next. Microscopic burrs around the mouth, inconsistent annealing, and carbon build up (or lack of any carbon) are common reasons for different neck tension.
Point is, far more things are going to mess up your game before small changes in bullet weight.
I don't think you have a big problem, even though it is good data.
From what I can estimate, a change in 0.5 grains for a 115 grain bullet would result in a 2.6 fps change or 0.2% variation in velocity.
Most ammo loads vary at least twice that according to my chronograph using high quality match ammo.
If you are using a very accurate scale, a 0.1 grain variation in Bullseye powder would create 10X that change.
From what I can estimate, a change in 0.5 grains for a 115 grain bullet would result in a 2.6 fps change or 0.2% variation in velocity.
Most ammo loads vary at least twice that according to my chronograph using high quality match ammo.
If you are using a very accurate scale, a 0.1 grain variation in Bullseye powder would create 10X that change.
ED tells you something about the sample. Assuming a normal distribution, SD tells you something about the population.
Put a different way, ED tells you something about the rounds you have already fired; SD tells you something about the rounds you'll fire in the future.
A separate point: SD has units; in the case of Chrono results, the unit is fps. So a given SD could be excellent for a higher velocity round and lousy for a lower velocity round. If you divide SD by Mean, you get Coefficient of Variability, a unitless percentage. This enables comparison between or among different calibers or loads.
Put a different way, ED tells you something about the rounds you have already fired; SD tells you something about the rounds you'll fire in the future.
A separate point: SD has units; in the case of Chrono results, the unit is fps. So a given SD could be excellent for a higher velocity round and lousy for a lower velocity round. If you divide SD by Mean, you get Coefficient of Variability, a unitless percentage. This enables comparison between or among different calibers or loads.