I have only been reloading for a year or so, but last night I went to the range to try out my new Chrony. For kicks I took my 22-250 along, just to shoot while the barrel cooled on my other rifle. Here is the problem I have. I ran 5 shots down to the target.
#1 3502 fps
#2 3543
#3 3423
#4 3570
#5 3537

They grouped very well but I am concerned about the 3423 fps load. I measure every charge out when loading, and according to my Sierra book I would have to have been off by a grain of IMR 3031 to slow the bullet down 100 fps. Is this common to drop 100 fps, or is 5 shots to small of a test group to worry about?

Regards
Rob

It is common and nothing to get alarmed about.

And 5 shots is not a lot of data. My personal preference is to have at least 10 shots and then calculate % standard deviation (standard deviation divided by average velocity multiplied by 100%). You see guys quoting SD for only 3 shots or 5 shots but it's not meaningful unless you have about 10 shots or more.

Now that you have a chrono you will gradually learn how to reduce the velocity variation. You may find that a different powder gives better SD, or that one powder gives a good SD in a certain pressure range and then SD increases at higher pressures. Different primers, neck tension, distance to lands, etc.

Not that SD is the most important factor in load development, but it's one more tool in your kit.

Great! I wasn't too concerned, but there are so many helpfull people here I thought I would just confirm it. I would also like to comment on some of the other threads that I have read, about new manuals being deluted down. According to Sierra 34.2 grns IMR 30301 should get me 3800 fps, I am no where near that, with this load. The Crony really opened my eyes.

zinger,

Your brass probably has more variance than your powder charges; weigh those cases.

As for your velocities, remember that many loading manuals contain results fired in match-grade pressure barrels with very uniform bores, not mass-manufactured barrels of dubious quality.

George

There are additional variables to consider. First, the primer. Have you ever considered that once in a while you'll get a bad primer? Second, the case. Some cases weigh as much as 10% more than others. They are flukes, but they cause fliers. Third, headspace. Some new cases have more headspace than others. Some have too much. Too much headspace allows the case to float in the chamber and lessen the impact of the firing pin.`This in turn affects ignition which affects velocity.

Why don't you weight-sort and neck-size the brass and repeat.

Ralph
All brass was weighed, and resized(full lenght). I agree with you on the primers, because I also had one round that would not fire at all. I also may have a head spacing issue, because after I posted this, I went back and looked at the brass, and I am getting some flattening of the primers. They are just slightly flat, and since I am no where near max velocity pressure should not be the issue.
Regards
Rob