I just got a Chronograph and was checking some loads over the weekend. These contraptions are really cool.
The calibers being checked are 6mm BR, .270.Win, 30-06, 7mm Rem Mag, 300 Win Mag and 300RUM.
The questions are:
1. What is an acceptable/unacceptable extreme spread?
2. What is an acceptable/unacceptable standard deviation?
3. Is it normal for two rifles of the same caliber, same length barrels and same load to have as much as 100+fps difference?
Thanks, *Nut*

Please disreguard this post. All I had to do was to wake up and do a search on the subject.
Plenty of info available.
Sorry y'all, *Nut*

[ 07-22-2002, 09:19: Message edited by: Nutoy ]

Now you've went and gone and done it (as my dad used to say as he was cutting a switch off the cherry tree)

Your new gadget will cause MUCHO head scratching and questions, like:
1. Hey, I thought I was supposed to get 3,000 FPS out of this combo (the chrono reads 2,850 or something)? That's a real shocker.
2. Wait a minute, these two rifles are exactly the same, how come this one gets 2,900 FPS and that one only does 2,800 with the same load?
3. Let's see, low SD = most accurate, but, this load with a HIGH SD shoots way better than that one with low SD. What's the story here??

Chrono's are a lot of fun, but, they definitely raise more questions than they answer. I use mine mainly for load comparisons or to get initial trajectory info, and quit trying to answer the questions they raise a long time ago.

R-WEST

Standard deviation and range ("extreme spread") vary with cartridge type and barrel length. For most rifles, a standard deviation of 35 fps is about normal with commercial ammo. With careful handloading, the high teens to low 20's are fairly easily obtained, though I'm not sure it makes a lot of difference in accuracy. My 29" Swede turns in low to mid teens, with no special care at all.

For groups of 3, the range divided by 1.69 is a good estimate of standard deviation. For groups of 5, divide by 2.33.