Do you normally see the ES's and SD's slowly improve or can they jump right to spectacular? I just ran a test with a new powder/bullet combo that was running high teens low 20's for the first 4 strings of 10. Then, in the last string 3/10ths of a grain higher, fell to an ES of 4 . I can't remember such a drastic change. I'll likely run that load again for peace of mind but wanted to get some expert opinions.
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Question about SD's and ES's
- Thread starter jambau
- Start date
ES = 4 is I think an anomaly....I’m anxious to see your follow up post to confirm or deny
SD = 4 would be phenomenal, and ES is usually 5-6 times your SD.....
SD = 4 would be phenomenal, and ES is usually 5-6 times your SD.....
I'd say most likely anomaly, but never know. If you really want to know what is real, do 25 shots. 5x 5 shot groups. That will give your "real" SDES speeds.
10/25 is fine. 6/12 is nice, but honestly, in a 25 shot test, expect 12/30.
10/25 is fine. 6/12 is nice, but honestly, in a 25 shot test, expect 12/30.
Agreed. Today I'm loading up a string of 25 for testing this weekend. Would really be awesome if the numbers hold up. Most of my other set ups run in the teens and I'm fine with that. It's rare that I get to shoot past 1k so i don't waste time and components looking for "holy grail" loads. But I'd certainly be ok if it settled in single digits.
An ES of 4 in a 10 shot string would indicate a SD of 2 or less is extremely unlikely. Just random errors are likely to give higher numbers. Are you sure the chronograph picked up all shots?
You are correctly planning on retesting.
The more rounds sampled the higher the ES will go while the SD will change much less as ES is defined by two extreme values and are less representative in a larger sample.
You are correctly planning on retesting.
The more rounds sampled the higher the ES will go while the SD will change much less as ES is defined by two extreme values and are less representative in a larger sample.
Assuming a sample size of 10 and a SD of 4, you have entered “The Twilight Zone” of Statistics! I would be surprised if it’s real, but even if it is, I’d be even more surprised if its repeatable.
Most chronographs are at best 0.1% accuracy. At 2500 fps, that’s a +/- 2.5 fps accuracy on each measurement. So the best SD its reasonable to expect about 1.25 fps if all velocities were the same. To load 6 rounds to +/-4 fps of the mean and another 3 or 4 to +/- 8 fps is possible but not probable.
The predicted 95% confidence interval for this SD is 2.8 to 7.3 for a larger population. If you test again and your SD is in this range you know its likely real.
Good luck!
Most chronographs are at best 0.1% accuracy. At 2500 fps, that’s a +/- 2.5 fps accuracy on each measurement. So the best SD its reasonable to expect about 1.25 fps if all velocities were the same. To load 6 rounds to +/-4 fps of the mean and another 3 or 4 to +/- 8 fps is possible but not probable.
The predicted 95% confidence interval for this SD is 2.8 to 7.3 for a larger population. If you test again and your SD is in this range you know its likely real.
Good luck!
Those are similar numbers to what I got using Hornady black factory ammo 140 gr 6.5cm. Not great but good enough for PRS type shooting.
That sounds more reasonable. If the SD and ES are for 25 rounds you’ve done a good job on consistency.
77 gr SMK w/ 23.8 gr H4895 14.4” barrel. Not awesome but decent in a gas gun. About 1 MOA.
Db2000,
That 25 round sample tells you there is a 95% probability the true SD is between 14.4 and 25.7 and the true mean is between 2582 to 2598 for similar rounds (the population) that your sample represents. That is a statistically significant test.
That 25 round sample tells you there is a 95% probability the true SD is between 14.4 and 25.7 and the true mean is between 2582 to 2598 for similar rounds (the population) that your sample represents. That is a statistically significant test.
@Doom Thank you for the knowledge bomb. I wish we could get everyone on the Hide to understand that until you accurately define the variance around the mean using a meaningful sample size, the mean is meaningless (no pun intended).
Guys are wasting time and components chasing phantom numbers that aren’t real.
A start would be to accept that flat spots don’t exist until you reach high pressures. So stop looking for them.
Dumbo’s feather
Guys are wasting time and components chasing phantom numbers that aren’t real.
A start would be to accept that flat spots don’t exist until you reach high pressures. So stop looking for them.
Dumbo’s feather
