Glock Talk banner

Acceptable maximum spread

1026 Views 14 Replies 12 Participants Last post by  Windjammer
What do you consider acceptable maximum spread in velocity for the various rifle and pistol calibers you load for?

How many rounds do you fire to get an average? I've heard everywhere from 3 to 20. What say you?

What's the best you've achieved?
1 - 15 of 15 Posts

· Registered
Joined
·
2,316 Posts
What do you consider acceptable maximum spread in velocity for the various rifle and pistol calibers you load for?
How many rounds do you fire to get an average? I've heard everywhere from 3 to 20. What say you?
What's the best you've achieved?
I will tell you my process for my pistol reloading as to what velocity range I look for. First you need some sort of base line data or standard in which you can measure what you produce.

Lets take a popular caliber for an example - 9mm fired from my G17 w/4.49" barrel. First I purchase 3 boxes of factory ammunition (124g FMJ RN) to obtain a base line for my reloading data. I fire 6 rounds for an average. I feel 6 to 10 rounds (max) is more than sufficient to obtain an accurate average.

Federal "American Eagle - 1,044.6 fps
Remington (green.white box) - 1,098 fps
Winchester USA (white box) - 1,039.1 fps

take the average of these - 1,060,5 fps / now you have what the average velocity from what the commercial ammo people are producing. In this case for your general target use I now have a "target" velocity to start with. Now you just decide for your self based on your own test results what is "acceptable" to you.

In this example the accuracy will dictate the final outcome but I will try to keep it in-between 1,040 & 1,080 fps




 

· Ninja
Joined
·
2,787 Posts
For pistol I usually shoot 15-20 rounds over a chrono. An extreme spread of 20-25 fps is acceptable for me.

For rifle I usually shoot the same over a chromo after I find an accurate load. For short range ammo ES under 25 is acceptable. For long range ammo an ES of 10-15 is max. Most of my long range ammo where powder has been measured with my Prometheus and case necks have been annealed, single digit ES is the norm.

Chronographs are not really used for checking rifle velocities for me. I am mainly checking ES/SD. I will get a rock solid 100 yard zero (400 for 50 BMG) and then shoot some groups at 600/1000 and see exactly what I need for come ups. Then when I get home I just work the data backwards for come ups to find out exactly how fast the bullets are going.
 

· Registered
Joined
·
1,226 Posts
I use 5rds to get an average velocity when working up a load for pistol, 10 for rifle, however more rounds will give you a more accurate average. Some powders are more consistant than others. Power Pistol and BE-86 have been the most consistant pistol powders I've used so far, often giving me spreads of less than 20fps, dropped from my Lee pro auto disk. My best shooting rifle loads also have an ES of less than 20fps. I trickle all my rifle loads. Often ES will shrink as you aproach max charge weight. I let group size dictate my loads. 50fps spread is no big deal for my pistol plinking loads using Unique. They're still plenty accurate for my purposes. However, a rifle load that varies that much probably isn't going to cut it for me.
 

· Registered
Joined
·
18,795 Posts
In general ES/SD is only critical when I am shooting longer range rifle. As phonejack points out, groups matter more than statistics, but there is a correlation as you move out in range. I also find that ES and SD give me a pretty good idea what is going on internally. It is hard to get good ES/SD numbers if a powder is being loaded at suboptimal pressures and densities.

For rifle, most of my pet loads are single digit SD, regardless of the range I shoot them at. I did have an occasion where I stumbled upon a load range in 308 Win with ARComp where I achieved zero SD in multiple 5 shot strings (pretty low ES too ;) ). Too bad those loads didn't fall on a nice node as the groups, while decent, were not excellent.

For pistol, in general, lower ES means the powder is working in an appropriate pressure range. I am not sure I have ever seen a big correlation between low ES/SD and greater accuracy. Although I can't say the correlation is perfect, in general, it seems the lower the ES the cleaner a powder will burn (usually because you are pushing pressures up into its optimal zone, I think). In pistol, if I am trying to achieve excellent accuracy, first comes the bullet, bullet quality has a pretty big impact on accuracy in my experience. Next on the list is recoil, lower is better (at least after the first shot ;) ), after that it usually is about having just the right amount of coffee that morning.
 

· Registered
Joined
·
40,421 Posts
Groups trump spread, simple as that
Agree, some get too caught up in the numbers. I use Std dev, 5rds min. If I can get single dig for rifle, great, but still doesn't mean it will group the best. For pistol, anything under 20fps w/ mixed brass is fine & that is mostly to make sure I make PF.
 

· Señor Mombo
Joined
·
2,909 Posts
Yup. Single digit ES is the goal. Some powders, in some cartridges will achieve this. But, always remember, that internal ballistics is only one part of accuracy.
 

· Registered
Joined
·
184 Posts
Yup. Single digit ES is the goal. Some powders, in some cartridges will achieve this. But, always remember, that internal ballistics is only one part of accuracy.
OhYes! while I try to get the ES/SD numbers as close as possible, that is only part of the accuracy equation, even if the numbers are very low barrel harmonics play a part in accuracy, In reality the biggest variable is the trigger puller, as in consistency in ammo performance it is even more so with firearm handling, especially as range increases
 

· Registered
Joined
·
40,421 Posts
Depends on how well it shoots. ES and SD are not the final word on how accurate a load will be and at close ranges almost don't matter at all.
I know a lot of guys that chase the number; runout, SD, ES, but it always comes down to groups size. Some of my best numbers don't shoot as well as loads with a little more ES or SD. So I don't chase numbers. Work the load up, shoot it, that is the proof in the load. You can always tweak it to get the ES/SD down but if the load shoots, it shoots.
 

· Registered
Joined
·
44 Posts
I go by standard deviation. IMO, it's the best way to measure variance.
For AR15, my rule of thumb is I want to see sd numbers below 20.
For pistol my rule of thumb is numbers below 23.
I have recorded numbers in the 7 to 8 range. When that happens I'm very happy. There may even be some lower numbers. But I have recorded a LOT of chrono tapes; too many to look through right now.

Forgot to add: I always shoot ten shot strings in order to get my sd numbers. (I'm glad I don't do very much reloading for .30cal! ;-))
 
1 - 15 of 15 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top