standard deviation

Well, Zero comes to mind! Seriously, I've had loads that have tiny SD's, on the order of 3-5fps, and they shoot good, or shoot okay. I've also had loads that have larger SD's, on the order of 12-16fps, and they shoot good, or shoot okay. In all reality, I look at SD like I look at primers - by itself, not a great indicator. Find an accurate load, though, and it turns out over time to have a small SD, and that gives me a great deal of confidence that in the field it will perform at distances as I expect it to. Of interesting note, my best shooting load in my best shooting rifle has a SD of just under 13fps. It is always under .5" (unless I call a flyer), and sometimes under .25". I have another load in that same rifle that has a SD of just over 5, and it is a 1.5" load all day, every day. The reality is that we cannot shoot enough to really begin to get a good sample size to really use SD as a hard data point. It's just an indicator of what might be a good load or not for most handloaders.
 
I have been using a chrony for about 5 months now and have found it indespensable to say the least.
S.D. in my opinion is nice to know. It seems kind of apparent that a load will shoot more consistantly based on the sd. The lower the sd the more consistant load you have but......sometimes your load may end up being a consistant one you wish you had in the morning.
I have had low sd's that didn't group well. I think that barrel "timing" has a a lot to do with group size and if you can find a load that groups well (good barrel timing) along with having a low sd or (a consistand load) you have found gold. The two kind of go together.
Just my $.02
 
I have a chronograph tape with a zero SD stapled to a target with the 1.5" group it shot. SD is more important the farther out pass 300yds you plan to shoot. I look at it as an indicator of how good the powder burn was for that load. I want to find a good group with a single digit SD or one in the low double digits, less than 20. I will not ignore good groups just because they have a higher SD, normally don't shoot more than 300yds.Rick.
 
rick smith, I agree with you for sure on the smaller SD preforming well at 300yds and beyond. I have had loads that shot great groups at 100yds and not real good past 250 to 300yds and had double digit SD. Yet on the other hand I have had in the same rifle and same bullet, using a different load not be as tight at 100yds as the group that did not shoot well past 300yds and yet would do much better on the longer shots and it's SD would be 10 and under. Now this was what generally took place in 90 plus percent but not in all of my examples and testing. As Guy, POP, GD338, Antelope-Sniper have indicated that single digit SD is the best thing to look for. As dubyam said we can't shoot enough examples to get a for sure data control figure to work from so it is in our best interest to stick with loads that do have a very low double digit (15 and under) while trying to obtain single digit. It seems to point to the fact that for most cases the single digit SD produces consistent barrel harmonics as old #7 has suggested. What would be cool is that you guys note this over the next year and then after hunting season this year publish your findings and lets see if we all come up with some kind of common denominator. :grin:
 
Bullet,

Your idea sounds great . While we are discussing SD i think we should also discuss components and tips that lead to really lows SD's. I myself am not a completely advanced or experienced reloader so i of course would be all ears.
 
craiger40":2ekh9uld said:
Bullet,

Your idea sounds great . While we are discussing SD i think we should also discuss components and tips that lead to really lows SD's. I myself am not a completely advanced or experienced reloader so i of course would be all ears.
Click to expand...

There are a lot of variables, such as the components we use, how they are assembled and with what equipment. This causing variables to be to great and cost prohibitive for real research. So that said, if we just all do our thing our way with our components and equipment to the best of our abilities we just might find a common denominator from among our examples to say there is one very important aspect that stands out when it comes to low SD and it's impact upon accuracy. Other than that it would all but be impossible to really quantify all the factors but I believe we for practical uses could get a sense of what really matters for a general conscience of the impact of low SD.
 
what about stuff like primers some people believe that certain primers are more consistent than other any truth to this.
 
Primers can make a huge difference. COL can make a huge difference.
The amont of volume the powder charge takes up in the case will affect things also.
I have found that the primers and col will affect sd the most.
 
craiger40":33oyhqr0 said:
what about stuff like primers some people believe that certain primers are more consistent than other any truth to this.
Click to expand...

This has to do with components again. Some say Fed, some say CCI, some say Remington and some say Winchester. What happens a lot of the time is that someone is getting good results with a primer and sticks with it as well as claiming there is none better. I think the difference is not as noticeable as some want to believe it is, although there is a difference and it can be a benefit depending upon type of shooting demanded like hunting, target competitions and the likes. For instance, I have shot all of my tight groups over the last two years with 250 CCI in my magnum rounds. I have also done pretty much the same with Fed 215 mag primers. There are just to many variables to consider and not go nuts or spend a ton of money and time. If I find something that works well in components, equipment and methods when reloading, I try to stick with it and be satisfied if it is doing the job I am asking of it.
 
old#7 you have made a great point. COL and primers I have found do make a difference in SD in the limited testing I have done once I starting using a Chronograph years ago and I think COL and primers really impact accuracy.
 
Primers are a bigger deal then most people realize. They must be matched to the powder, and the size of the charge. You need cold primers for stick powder, and a hotter primer for ball powder.
 
Well here is another one how about ambient temperature. I guess you could better describe it as powder temperature sensitivity. Yesterday while at the range i noticed that my loads that i shot in the morning were a little more deviant during the higher temps of afternoon. This could be a problem here in texas. When i started shooting around 9am the temp was around 63 degrees
at noon it was around 87 degrees. I was shooting loads using RL-19,RL-22. Does anyone have any insight as to how well these powders perform at various temps?
 
RL-22 has a reputation of being temp sensitive. I don't know about rl-19.
I do know that temperature, air temperature or you just fired two or three rounds then chambered another round but didn't shoot it for a minute(put it in an oven), does directly affect velocity and of course sd.
 
Consistent neck tension. All cases properly sized and trimmed. This can contribute to low SD numbers.
 
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