What's a good standard deviation for muzzle velocity of reloads?

[flintlock.50]

I've been loading for decades, but only relatively recently obtained a chronograph, so I don't have much experience on how consistent the muzzle velocity of my reloads is. I can certainly recognize a really good standard deviation or a really bad one. But what is considered "good" for typical rifle and handgun reloads. I'm NOT talking about what's acceptable to a competitive bench rest shooter, but what is considered "good" with good quality components, weighing each powder charge and careful, but not obsessive, attention to detail (say using the 80/20 rule).

Thanks

 

[hounddawg]

First off if you are shooting at or less than 300 yards don't sweat the SD. Find a accurate load and use the chrono for bullet drop calculation and have fun.

Even at 500 and out you don't have to be obsessive if you find the right powder and bullet. The trick is to find wide flat nodes where you can be off .1 gn either way and have relatively small changes in velocity. Smaller cartridges are more finicky than large. Finding the right powder and bullet weight/brand is the key. Find out what others are using, keep a open mind, and don't get locked in on a certain bullet or powder if it is not working.

Good luck

 

[RaySendero]

flintlock,

I keep records velocity X-Spread,
Standard Deviation (SD) and
Coefficient of Variation (COV)

I prefer the Coefficient of Variation more than Standard Deviation.

COV is easy to figure:
Just divide the SD by the average velocity and express as a percentage.

I like to see the COV less than 1%.
I have attained some batches of reloads less than 1/2 %.

 

[Jim Watson]

Agree. A PhD in my office took an interest and pronounced pistol ammo at 1% real "match grade."
Target rifle ammo is less.
Black powder properly loaded is very consistent and you need less than 1% for BPCR.

 

[74A95]

With handgun ammo at the usual handgun distances, s.d. is irrelevant. It predicts nothing and is only useful for competitors trying to make power factor where a smaller s.d. helps to insure that their ammo won't deviate too far from their average speed and accidentally move them below major or minor power factor.

For other purposes, it might be useful to help insure that bullets don't fall below a certain speed to help ensure the chance that a HP bullet will expand.

But s.d. does not predict how accurate a handgun load will be. Some powders that produce the best accuracy have the widest s.d.s. So good, bad, whatever s.d. has no meaning. If you're pursuing accuracy, ignore the s.d. and pay attention to the target.

And see this article that tests group size and s.d. in a handgun: https://americanhandgunner.com/handguns/exclusive-consistent-velocity-accuracy/

There was no correlation between group size and s.d.

 

[std7mag]

For my use, mostly hunting rifles but lots of target shooting i try for ES of under 15 fps, and SD of under 10 fps.
As Hounddawg says, under 300 yards your really not going to notice too much. Stretching your legs to 500-1,000 yards is where your going to notice it.

 

[flintlock.50]

Thanks. Good info, all.

 

[RC20]

Yep. Lower numbers are an indicator (Indicator only) of a good reload process of fine details.

It does not mean the lowest numbers are the most accurate.

In the end its a combination of the Indian, the arrow and the bow.

 

[Bart B.]

If bullet departure from the muzzle is at the right place on its upswing, velocity spreads can be compensated for and reduce or mostly eliminate vertical stringing on target.

 

[rclark]

In handguns I like to see ES under 50fps. And that is with a 10-15 cartridge sample. FYI, statistically SD needs at least a 10 round sample to be meaningful. I usually shoot a string of 15. As said above a low ES does not mean it will always be accurate .... but it always help, never hurt.