Best practice for chrono'd rounds

[G17fan]

Hello all.... What's the best way to determine the FPS to calculate PF?

4,8,10.... Rounds to get the average?

Thanks.

[bassochist]

i always shoot 10 rounds, and also look at the standart deviation, from the sd you can determine how constant your rounds are.

with less than 10 rounds, you can't determine the standart deviation correctly.

Edited September 23, 2012 by bassochist

[Sarge]

i always shoot 10 rounds, and also look at the standart deviation, from the sd you can determine how constant your rounds are.

with less than 10 rounds, you can't determine the standart deviation correctly.

Agreed. I always shoot at least 10 at a time. And I generally chrono at least 100 rounds before I call a load good.

[sroe3]

I shoot at least 10, usually closer to 30. I consider the slowest rounds as most critical. With my luck those would be the rounds chosen to chrono at a match. Deviation and max, while interesting numbers, won't have me shooting for no score.

[Youngeyes]

When you shoot a string, make sure you shoot thru the same area of the chrono. You can have differences if you shoot high then low.

[Guest]

After developing and settling on a load the chrono'ing isn't over. I try to chrono 8-10 rounds every so often under different conditions.

This does two things, one it helps to learn if loads might be temp sensitive or change with the seasons, and two it helps to monitor the consistency of my loading components and technique. Another point is to weigh a fairly large sample of bullets (50+) and use the lightest bullet from that sample as your bullet weight in the PF calculation. I usually load with good margins from the PF floor with the intent that no chrono reading will ever fall below the power factor floor. There is no rounding up in the PF calculation, either you make it or don't (USPSA appendix C2).

[RePete]

The greater the number fired, the "better" the results.

I use 10.

[a matt]

i shoot 3 then cold tru the chrono, i shoot some practice then i chrono 3 just like a major. BUT i do it about 5 time at that practice session. i pay att. to the low FPS. write down temp, time, powder, everything about that round even brass. i have found different brass will cause major dev.

[bbbean]

I try to do a more strenuous version of the actual chrono procedure. Once I have a load I know is in the ballpark:

Step 1: Run 20 rounds over the chrono. Make sure average, "olympic average", and standard deviation are in the range you want (shoot for a little higher rather than lower)

Step 2: Average the fastest three of the slowest 7 rounds.

If my overall average and standard deviation are in the right ball park, and the fastest three of the slowest 7 make power factor, I figure I'm good to go.

Then I repeat with another 20 rounds, preferably on a day with different weather conditions.

The end result is that even on a slow chrono, I'm confident that I'm making PF with room to spare, and I've run a minimum of 40 rounds over the chrono (usually 60-80) by the time I've used the load for a while. The chrono is the one stage where I'm confident of making a 100% score every time!

[Hi-Power Jack]

I fire 20 shots and make sure that The Lowest number

is above necessary PF. Can't lose that way.

[OUshooter]

i shoot 3 then cold tru the chrono, i shoot some practice then i chrono 3 just like a major. BUT i do it about 5 time at that practice session. i pay att. to the low FPS. write down temp, time, powder, everything about that round even brass. i have found different brass will cause major dev.

I play a similar game. I will chrono the batch in groups of three to simulate a chrono stage. I will shoot anywhere from 5 to 8 groups. As long as the lowest FPS from each string gets me above my target PF I call it good. I will usually go through and group the ammo by headstamp. To date I haven't found a statistical difference. What I have found is that grouping by OAL will show a pattern, and the SD within a narrow ± range will be lower.

Edited October 1, 2012 by OUshooter