How many rounds do you chronograph?

[Shadow9mm]

When working up a load, how many rounds do you actually chronograph per charge weight to get your AVG, ES, SD.

Been reading a lot of interesting stuff in relation to ES/SD and the statistics of how many rounds you need to fire/chronograph to have data that you can consider dependable. But my question was more, what are we actually doing right in practice, not theory. I allowed 2 choices so that if people have different standard for pistol or rifle, or training vs precisions ammo and you have different methods you can list both.

For general purpose training loads and handgun loads I am generally shooting 10, for my precision/target ammo I am shooting 30.

[Rimfire5]

Using QuickLOAD and loading for exit time for all of my reloading since 2014, I have stopped using a chronograph.

I calculate exit time for each particular barrel (result depends on barrel length and the reflection time in the particular barrel steel).
Choosing loads that produce the desired exit time is supposed to reduce barrel harmonics and optimize accuracy. That's exactly what a lot of people use chronographs to do by shooting ladders.

My experience, to date, shows that starting with a desired exit time gives me pretty good results without having to guess.
Given that, I can tell if the loads are working by using the average group size of the first 5 to10 groups sent down the barrel.

My first session, last week, with a cleaned and sighted-in, new 26-inch 416R Shilen Select Match 1:7 twist barrel on my old .223 Savage 12 FV produced an average group size of 0.194 for six 5-Round groups of 77 SMKs with Varget powder with a standard deviation of 0.029.
I didn't need to chronograph that result to understand that the load was right on what I needed.

That was right out of the box, first time I shot that barrel for anything but breaking it in and sighting in the scope.
My experience tells me that my exit time approach does all I need to find what works.

[44 AMP]

I chose the "other" answer, because the number of rounds I chronograph is zero.

I did use a chronograph for several years, and what it taught me was that, for what I do, the numbers aren't very important. What matters to me is what the rounds do, down range.

As a friend of mine is fond of saying, "if it doesn't help me put an elk in my freezer using my .300 Savage model 99, its not useful to me".

what my chronograph taught me was that the actual speed (and the other variables) differs with each different gun, either by a little, or sometimes, a lot, from the published data. And, that unless your goal is maximum achievable uniformity, small differences are rarely significant.

[tangolima]

It is pretty complicated if you dive into the mathematical muck, namely statistical confidence interval. Here is an over simplified version.

We are trying to estimate the population mean and standard deviation with n samples. Such estimates come with uncertainty, or tolerance. The # of samples n tightens the tolerance. Most, if not all, of my loads has sigma/mean (coefficient of variance) <0.5%. With 95% level of confidence

n=3
Mean=sample mean +/-0.8%
SD=sample SD *(0.6 - 4.5)

n=5
Mean=sample mean +/-0.5%
SD=sample SD *(0.7 - 2.4)

n=10
Mean=sample mean +/-0.3%
SD=sample SD *(0.7 - 1.6)

n=30
Mean=sample mean +/-0.2%
SD=sample SD*(0.8 - 1.25)

For instance, last Friday I shot 10 rounds of .243 win. The 10 samples give average MV 2820fps with SD 14fps. The true MV is between 2812 - 2828fps. SD is between 10 - 22fps. However, if I fired only 3 shots, MV is 2797 - 2843fps, SD is 8 - 63fps.

More samples is of course better, but it is more costly. It is a balance to strike. For me n=10 is about right.

-TL

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[Aguila Blanca]

When I bothered to run reloads through a chronograph, I was doing five of each. Then I read multiple articles that said anything under ten wasn't statistically significant.

Obviously, the more samples you shoot, the more representative the averages will be. In the future, for anything that counts I think I'll regard 10 rounds as the sample population. As tangolima noted, it's a matter of balancing cost versus benefit.

[gwpercle]

Would you believe ... 0

Never owned or had access to a chronograph ...

I was much more interested in Accuracy than in velocity and Holes in Targets
told me everything I wanted to know .

I checked off "Other" ... hope that was correct !
Gary

[taylorce1]

Since I bought a Garmin, pretry much every time I shoot I chronograph. Except when I'm hunting. The reason I do this now is more data in, more data out. I even chronograph factory ammunition, that way I'll know how it'll perform in varying conditions.

[tangolima]

Originally Posted by Aguila Blanca

When I bothered to run reloads through a chronograph, I was doing five of each. Then I read multiple articles that said anything under ten wasn't statistically significant.

Obviously, the more samples you shoot, the more representative the averages will be. In the future, for anything that counts I think I'll regard 10 rounds as the sample population. As tangolima noted, it's a matter of balancing cost versus benefit.

I have seen promising 3-shot groups turned out to be dud after firing 7 more rounds, and vice versa lousy ones turn good. Here I don't take extreme spread, but mean radius calculated.

Also I need to resist the temptation of excluding unfavorable poi as flyer, unless I have called it correctly.

-TL

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[Aguila Blanca]

Originally Posted by tangolima

I have seen promising 3-shot groups turned out to be dud after firing 7 more rounds, and vice versa lousy ones turn good. Here I don't take extreme spread, but mean radius calculated.

Take any measurement you want. Take a box of .22LR -- 50 rounds to a box. The advertised velocity for CCI standard velocity .22LR is 1,070 fps. Does every round in a 50-round box produce 1,070 fps through whatever barrel they used as a test barrel? Of course not. I have no idea what their acceptable deviation is, but call it +/- 5%. That would mean that for each 50-round box they grabbed 50 rounds out of a production batch of many thousands, and any one of those rounds (each one of those rounds) could have a velocity anywhere from 1,017 fps to 1,124 fps. One box may, by pure luck of the draw, get a high percentage of "fast" rounds, and the next box may get a high percentage of "slow" rounds.

The fewer rounds you test out of that box, the less chance there is of getting a sample that accurately represents the true range for the entire batch that you're sampling. In reality, out of a day's production of .22LR even an entire box of 50 is likely not going to hit an average velocity of 1,070 fps. And if it does -- is it repeatable? In other words, if you pull three or five boxes out a production run and average each box as a sample set of 50 rounds -- would any of them average 1,070 fps? How close would the average of the three or five samples be?

[tangolima]

Originally Posted by Aguila Blanca

Take any measurement you want. Take a box of .22LR -- 50 rounds to a box. The advertised velocity for CCI standard velocity .22LR is 1,070 fps. Does every round in a 50-round box produce 1,070 fps through whatever barrel they used as a test barrel? Of course not. I have no idea what their acceptable deviation is, but call it +/- 5%. That would mean that for each 50-round box they grabbed 50 rounds out of a production batch of many thousands, and any one of those rounds (each one of those rounds) could have a velocity anywhere from 1,017 fps to 1,124 fps. One box may, by pure luck of the draw, get a high percentage of "fast" rounds, and the next box may get a high percentage of "slow" rounds.



The fewer rounds you test out of that box, the less chance there is of getting a sample that accurately represents the true range for the entire batch that you're sampling. In reality, out of a day's production of .22LR even an entire box of 50 is likely not going to hit an average velocity of 1,070 fps. And if it does -- is it repeatable? In other words, if you pull three or five boxes out a production run and average each box as a sample set of 50 rounds -- would any of them average 1,070 fps? How close would the average of the three or five samples be?

Not sure about ammo industry, but the sort of work we do, if any one falls outside 1070+/-5% at the specified test conditions, we can return the whole shipment.

-TL

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[Aguila Blanca]

Not sure about ammo industry, but the sort of work we do, if any one falls outside 1070+/-5% at the specified test conditions, we can return the whole shipment.

Agreed, but irrelevant. My point was that, assuming that +/- 5% is the standard, any round in a batch can be anywhere from 1,017 fps to 1,124 fps and be within spec. Out of tens or hundreds of thousands of rounds, any 50 randomly picked could be a representative cross-section, or they could all be 1,018 fps, or they could all be 1,123 fps. Out of a batch of 100,000 rounds, is even 50 rounds statistically significant? How about 50 out of 1 million?

[tangolima]

Originally Posted by Aguila Blanca

Agreed, but irrelevant. My point was that, assuming that +/- 5% is the standard, any round in a batch can be anywhere from 1,017 fps to 1,124 fps and be within spec. Out of tens or hundreds of thousands of rounds, any 50 randomly picked could be a representative cross-section, or they could all be 1,018 fps, or they could all be 1,123 fps. Out of a batch of 100,000 rounds, is even 50 rounds statistically significant? How about 50 out of 1 million?

Ok I see. For normal distribution, the population size doesn't matter. The sample mean and SD calculated will indicate the probability of a failed round with an associated level of confidence. For instance, it is 95% sure that 99.99% of the rounds will pass. The sample size determines the level of confidence. Say we want to be 99% sure, then we will need to increase sample size from 50 to 100 etc. I can see the reason to do that for large population as number of rejects is proportional to the population size, and each reject carries cost. That again is a balance to strike.

Note that we can never be 100% sure unless we screen every round. Then you fire every round off the line and nothing left to ship.

I know on the production line, the QC department is constantly sampling to calculate the running average. The frequency of reach depends on the production speed.

-TL

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[jrothWA]

usually fire 7 rounds over a1990-era Pact 1 chronograph.

I review the results and look at the "Std.Dev" results and look at the Extreme Spread results, for a final confirmation.

[Double Naught Spy]

I usually chronograph however many rounds it takes me to get zeroed anew with whatever new ammo I am using, so usually 3-7.

Update. Sighted in some new ammo. 5 rounds to zero this evening.

[stagpanther]

To each their own. We live in a golden age of factory ballistics where you can buy off-the-shelf stuff that can be very high quality across a wide range of guns. Sometimes I have a hard time beating some of the stuff in hand loads and it can take a lot work for a load that might only work better just in my particular gun. I chrono almost all my loads--I like to use the info to cross-check predicted results from ballistics software (and vice versa). Presumably the ED/SD numbers also help confirm a node for that load in your particular barrel. I don't get too hung up on the number of shots, though I usually shoot 5 to 7 for a particular charge weight. Once I find a good group "candidate" with tight ES/SD numbers I'll shoot 3 close charge weights at the same time--looking for very close results between the 3 groups as confirmation of the likely presence of a really good node. Every once in a while I'll have excellent ES/SD numbers but the grouping itself on paper might be terrible--often that indicates to me that there is a possibility that there might problems with the gun set-up.

[FrankenMauser]

{edit: you know the rules.}


As per the topic at hand:
I only chronograph handgun loads if I:
A: Need to meet a minimum velocity or power factor.
B: Need to know what my black magic load has created.
C: Want to know why something isn't functioning.

But when I do, I chrono a minimum of 5 rounds. Often, I do 10.

[ocharry]

i dont use a chrono to work up loads...i get the load working and shooting groups and then i might....might ...use the chrono to check velocity so i can have good data to put into ballistics for hold over or knob twisting...sometimes i just put it on targets at different yardages and get the true data... that way...when things are happening fast... sometimes you just got know what you need and forget all the fancy stuff...lol

when i get to a load that is working...and i use 5-10 shots for that...i will load up around 20 and check it with the chrono on 5 different days...5 shots...clean and wait till the next time..next day or it could be a couple days...but i check it 5 different times with a chrono because all i need to know is the true velocity...or a real good average from a clean cold barrel...all the rest for me is just smoke because i use that load on different days and that load could make different data tomorrow or next week so i need a running average...not all on one day...yeah my magnito speed tells me all that stuff...i just dont care...most of my shooting these days is 300 and in...and i am looking for good accuracy and a quick punch so all i need to know is where the bullet is gona land..how much hold over...once i get that i can take it to 250 or so and do a group check there too..and to see if the calculator is working good

hard punch on target is what i need from my rifles to 300

no fancy stuff...just DRT

[Nathan]

I chrono what ever I can. I chrono 2 if I’m shooting 2. I chrono 5 if I shoot 5. I don’t like to make decisions more than general velocity with less than 10 rounds. I prefer 20 for zero’ing and calculating drops.

[RC20]

I chrono all of them.

I may only refer to the data from time to time but I have it and at times I get a random high or low one, keeps me on my toes.

[RickB]

I'm almost always loading to a desired velocity, so if all ten rounds of a given load meet the minimum, I'm satisfied.
Sometimes, I'll chrono ten, throw out the low and the high, then average the other eight; I feel like that gives more of a true average without having to chrono 20-30 or more rounds.

[tangolima]

I used to discard extremes. It makes the data look better. Same for groups. I allowed 1 uncalled flyer out of 10 shots. The group looked tighter.

Now I have strictened the "policy". Data can only be discarded for a reason; cracked neck, correctly called flyer shot etc. Sample size is already marginal. Throwing out data doesn't help.

-TL

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[Nick_C_S]

I voted "10." But really, it depends.

If the load is so new and different than anything else I've done in the past, I may chronograph as few as two rounds. If the round is this experimental, there will be no other charge weights to test the first time out with the chrono. It's back to the load bench after just the two recorded velocities.

Once I have some idea what I'm dealing with, I'll often go with five (or six, because revolver friendly) - just to get the load in the right neighborhood.

Once I'm getting it narrowed down, I'll go with 10 round samples - sometimes 12 (what can I say, I'm a revolver guy .)

The last time I chronographed (three weeks ago), I was doing just one charge weight, but it was an 18 round sample. It was a 38+P with a really fast powder (N-310) and I wanted to make sure I wasn't getting any spikey outliers.