Typical Pistol velocity St. Dev. & Extreme Spread

[Unclenick]

Originally Posted by tangolima

SD or ES without MV has little meaning...I'd like to keep this below 1% for my loads.

Well, keep in mind there are SDs for pressure and group size variation, too. But you are correct that SD and ES have to be in the context of the mean value. The technical term for the SD as a percentage of the mean is the Coefficient of Variation (CV). All of SAAMI's pressure testing numbers, for example, have their limits based on a CV of 4% for centerfire rifle and rimfire ammunition, 5% for centerfire handgun cartridges, and 7.5% for shotgun shells. I don't know why chronographs don't give the CV as a standard feature, as it seems like an obvious thing to do. But we are left to work it out for ourselves.

[zeke]

Originally Posted by Unclenick

Zeke,

You probably changed the barrel time with the tight crimp. You may also have distorted the bullet with it. Either one can throw accuracy off. That's not the fault of the ES.

You betchca the bullet was distorted, but the purpose was to get as consistent velocity's as possible, not work up accurate load. For my own satisfaction. Not blaming the ES, but demonstrating consistent velocity's are not automatically associated with smaller groups. Some prefer to refer to their statistics, instead of how accurate the load is. For my purposes, consistent velocity's mean nothing unless precision accompanies the numbers.

Am not a statistician by any means, but federal guidelines stated not to use LP III unless 20 relevant data points were available. Granted those were flow analyzes, from older times.

[Shadow9mm]

Originally Posted by zeke

You betchca the bullet was distorted, but the purpose was to get as consistent velocity's as possible, not work up accurate load. For my own satisfaction. Not blaming the ES, but demonstrating consistent velocity's are not automatically associated with smaller groups. Some prefer to refer to their statistics, instead of how accurate the load is. For my purposes, consistent velocity's mean nothing unless precision accompanies the numbers.

Am not a statistician by any means, but federal guidelines stated not to use LP III unless 20 relevant data points were available. Granted those were flow analyzes, from older times.

in handguns its a bit harder, but its on my to do list to try. When working up a load, I shoot for the best SD and ES. What I have found is that that, by tuning the seating depth, usually in 0.003 increments, I can get the accuracy where I want it, rather than trying to do it with charge weight. Its all about timing when the bullet leaves the barrel at a consistent point in the barrels harmonics. I feel tuning seating is a much better way to do that than with the powder charge, but that's just me.

With 9mm I think I may be able to do it. with my revolver cartridges that I crimp into a groove, I am not sure how to go about doing that. I have a few irons in the fire to deal with before I get to that project though.

[GeauxTide]

10 shot strings will tell the tale. If your Chrono doesn't have a printer, write down velocity of each round.