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How many rounds do you chrono when testing?


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My searching found nothing on this since 2011, but prior to that it seems folks were shooting 4 or 5 rounds to ball park their loads, then a couple of 10 shot strings to verify once they dialed in a load.

 

With my Shooting Chrony, I always shot 1 or 2 ten shot strings when I wanted to chrono a load.  I would shoot a couple of strings through 4 different guns (Glock 34 & 17, STI, and Ruger PCC).

 

I just recently upgraded to a ProChrono DLX and now that I have the ability to log to my iPhone I'm planning to change it to one string of 15-30 rounds for each gun.  This also coincides with my making the switch from copper plated bullets to coated bullets due to availability and cost.  So, when working up a new load, or just verifying your tried and true load in a new gun, how many rounds to you run over the chrono to be satisfied of the result?

 

Thanks,

-Cuz

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I do the same as above, 6 rounds for chrono. If I'm happy with the PF, I would shoot another 6 to confirm cycling/ejection, and another 6 to confirm accuracy/zero from various distances. If all is good, then it's time to mass produce 😃

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15-30 is alot, BUT your average,ES, and SD will be more accurate. Not sure how good it needs to be though.  ROundcount depends on what I am doing though. If I am doing a ladder I might be happy with 3 rounds each.  Upsets the neighbors less.  Load 3 shoot em, load 3 shootem. Get what I want then go load 5 more to verify. Usually though my loads arnt exactly new, or uncharted territory. Been doing this a long time. So I generally can get pretty close to velocity I want before I hit the chrono. Usually I am just fine tuning for a particular gun.
I have been shooting alot more 45 though and this is only my first year loading much for it. Also none of my loads really match what others on this forum are using, as its for a different game, and I am loading in the 195 pf area and with a 6" barrel.  Which does kinda bumm me, as I just learned there is a 7 out there.

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You only need 8 rounds to get a good statistical measurement (avg vel, SD).   The question is what do you do with it?  How does that relate to an official power factor check?  You cant use your measured statistics directly to know if you will pass the official PF check.   Here is why and how to use your measurements.

 

 

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9 hours ago, jwhittin said:

You only need 8 rounds to get a good statistical measurement (avg vel, SD).   The question is what do you do with it?  How does that relate to an official power factor check?  You cant use your measured statistics directly to know if you will pass the official PF check.   Here is why and how to use your measurements.

 

 

Basically I agree. I generally shoot two separate magazine loads of 20 rounds each. (With lower count mags I shoot 20 test rounds by whatever means necessary). Out of this I would expect to see each test to have a SD of 5 and absolutely under 10. I also expect the individual tests to agree within 2 PF's and usually +/- 1 PF.

 

The Z test above is interesting but not necessary. Keep in mind that statistically in a normal distribution of numbers +/-1  SD represents 68% of the population of the sample and +/-2 SD represents 92% of the population. While I'm not claiming we are dealing with a normal distribution, we have little chance of dealing with anything else mathematically. 

 

So if a get 167 Avg of 20 rounds with a 7 SD my actual sample predicts 68% of my rounds will fall between 160 and 174 68% of the time. That does not give me a strong chance of passing chrono when they shoot 3 rounds. No way I spend a bunch of money and time betting on success here.

 

So how about a 172 avg with a 7 SD. that looks a lot better but still leaves a nervous feeling when only looking at 3 rounds. Im not a lucky person.

 

I just finished approving my load for an Area match. I got two 20 round samples to agree perfectly at 173PF. One was 5 SD the other 6. So using the 6 I easily show 68% of my rounds are between 167 and 179 and 92% are between 161 and 185. I think I can live with that because the chance that chrono pulls two of 3 rounds below 165 is terribly small.

 

Frankly I would add that I have another criteria. I don't want any round of the 20 round test to fall below 165. So actually no matter what the math says I don't want any failures in my test. I have never failed chrono and I am not going to take a chance. Im still nervous though.

 

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17 hours ago, Brooke said:

So how about a 172 avg with a 7 SD. that looks a lot better but still leaves a nervous feeling when only looking at 3 rounds. Im not a lucky person.

Exactly!!! and that is the whole point of using the Z parameter and SD, not PF (as explained in my article).   The Z parameter is based on the statistics of using 3 rounds for pass/fail (P/F).  It takes into account your actual average velocity and SD ( measured using 8 rds) and provides a P/F confidence level as a guide).  Once you go below 8 samples, you should use the T or Student distribution or your results will be skewed.   Case in point, if you add 1SD to your avg velocity, as you stated the Normal dist tells you 68% will be within +/- 1SD  (32% outside).  But if the P/F criteria is determined using 3 rounds the Normal distribution doesn’t apply and your change of failing is actually about 44%.

 

17 hours ago, Brooke said:

While I'm not claiming we are dealing with a normal distribution, we have little chance of dealing with anything else mathematically. 

Not true.  There are many different distributions who's statistics are well known (too many to list).  The difficult part is determining which one applies to the case at hand. 

 

Final point - you will not see much variation in the measurements after you get 8 or so samples.  The improvement is insignificant for our application.  More than 8 to 10 samples is a waste of ammo.    You can test this for yourself. 

 

 

Edited by jwhittin
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I have no problem with your Z test. Its actually pretty useful. My comments were only directed to explain the results. Someone just looking at some mysterious "factor" might not believe your Z.  Tying it to a more common statistical number might improve acceptance.

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I understand that you probably don’t need to shoot 15+ rounds over the chrono, but I figure if I have to Haylee it to the range and set it up, I may as well send some extra rounds over it.


Sent from my iPhone using Tapatalk

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23 hours ago, Brooke said:

Basically I agree. I generally shoot two separate magazine loads of 20 rounds each. (With lower count mags I shoot 20 test rounds by whatever means necessary). Out of this I would expect to see each test to have a SD of 5 and absolutely under 10. I also expect the individual tests to agree within 2 PF's and usually +/- 1 PF.

 

The Z test above is interesting but not necessary. Keep in mind that statistically in a normal distribution of numbers +/-1  SD represents 68% of the population of the sample and +/-2 SD represents 92% of the population. While I'm not claiming we are dealing with a normal distribution, we have little chance of dealing with anything else mathematically. 

 

So if a get 167 Avg of 20 rounds with a 7 SD my actual sample predicts 68% of my rounds will fall between 160 and 174 68% of the time. That does not give me a strong chance of passing chrono when they shoot 3 rounds. No way I spend a bunch of money and time betting on success here.

 

So how about a 172 avg with a 7 SD. that looks a lot better but still leaves a nervous feeling when only looking at 3 rounds. Im not a lucky person.

 

I just finished approving my load for an Area match. I got two 20 round samples to agree perfectly at 173PF. One was 5 SD the other 6. So using the 6 I easily show 68% of my rounds are between 167 and 179 and 92% are between 161 and 185. I think I can live with that because the chance that chrono pulls two of 3 rounds below 165 is terribly small.

 

Frankly I would add that I have another criteria. I don't want any round of the 20 round test to fall below 165. So actually no matter what the math says I don't want any failures in my test. I have never failed chrono and I am not going to take a chance. Im still nervous though.

 

But what if they take the highest 3 velocities of 7 rounds (per item 37 and 38 of appendix C2) to do the calculation?

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8 hours ago, caspian guy said:

But what if they take the highest 3 velocities of 7 rounds (per item 37 and 38 of appendix C2) to do the calculation?

Per 37, one additional round is used.  Could improve your chances or make things worse.  It's a gamble.  

 

This is why I calculated the Z parameter using only 3 rounds.  I didn't want to worry about what happens next. 

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34 minutes ago, jwhittin said:

Per 37, one additional round is used.  Could improve your chances or make things worse.  It's a gamble.  

 

This is why I calculated the Z parameter using only 3 rounds.  I didn't want to worry about what happens next. 

That's not the way I read that..   They take 8... Pull 1 to weigh.  Then they shoot 3.  Then if you don't make it they shoot another and take the 3 highest... If that doesn't make it they do it again and recompute.  If that doesn't make it you have a choice on the 7th.. You can have them pull the bullet and weigh it... Or shoot it.   The result is your attempt to make pf is actually based on the average of the highest 3 velocities  out of 6 or 7 rounds depending on what you elect to do with the last round.  Look at the part at the end where it talks about this will continue...

Edited by caspian guy
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On 8/22/2020 at 8:21 AM, Cuz said:

My searching found nothing on this since 2011, but prior to that it seems folks were shooting 4 or 5 rounds to ball park their loads, then a couple of 10 shot strings to verify once they dialed in a load.

 

With my Shooting Chrony, I always shot 1 or 2 ten shot strings when I wanted to chrono a load.  I would shoot a couple of strings through 4 different guns (Glock 34 & 17, STI, and Ruger PCC).

 

I just recently upgraded to a ProChrono DLX and now that I have the ability to log to my iPhone I'm planning to change it to one string of 15-30 rounds for each gun.  This also coincides with my making the switch from copper plated bullets to coated bullets due to availability and cost.  So, when working up a new load, or just verifying your tried and true load in a new gun, how many rounds to you run over the chrono to be satisfied of the result?

 

Thanks,

-Cuz

Cuz:

 

I do the 10 round strings using 11 rounds; first round into the berm to settle the pistol in.  Using the Pro Chrono with the Bluetooth adapter coupled to my iPhone.  

 

This is just my routine, and I enjoy doing it this way.  Attached is a sample of 6 runs that really helped me get a feel of using the App and having it call out my numbers.  Probably didn't need this many runs, but I was having fun doing this!  

 

;)

Reload Chrono Results Round1.pdf

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I typically will load 10 for each increment... fits case evenly/across and also gives a couple extra just in case I get any misses with the LabRadar or get a high/low spike for some reason..

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How many will be determined by what I'm trying to achieve.  Since you just about about chrono, if I'm doing load development, then 10 rounds per charge.  If I'm just trying to verify a load, then 5 rounds.  lastly, to verify power factor, then 3 rounds are used. 

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So it definitely sounds like I’m overdoing it a bit. But I rarely drag out the chrono, so when I do, I figure more data must be better...


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On 8/27/2020 at 3:43 AM, stick said:

... lastly, to verify power factor, then 3 rounds are used.

 

The problem with using only 3 samples is that the variation between measurement sets can make it very difficult to reach conclusions about your Avg Vel and STD with an acceptable level of confidence.   If you take 3 or 4 or 6 data sets of 3 rounds each and calculate and compare the statistics (avg vel, STD, spread) for each set, you will see what I'm talking about.    The results are all over the map.   That is why I did the analysis and determined the Z parameter which relates 8 round measurement results to a confidence level of passing the PF check with the first 3 rounds.  

 

 

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when I get my notebook I am gonna take you up on that,,,  my 45 pin load I have chrono'd a couple times at different temperture to see if it mattered all that much (it didnt)  Can grab a handful of random 3 shot samples and see what I get.
I suspect. It wont amount to squat in difference. As my ammo is decent and is pretty consistent.

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I have always shot 15 rounds over the chrono...  The 15 round average is a good predictor of the overall load power factor...  and I can look to see how far any fliers fall from the core area...  While you can get by with chronoing three rounds (as that is all the chrono RO will fire if they all pass)...  Selecting only three rounds out of 500 rounds for a match might not give a clear picture.

 

Have a somewhat new Pro Chrono DLX...  It is listed as more accurate than the old model...  I don't know about that...  I bought it mainly for the Bluetooth connectivity...  Nice to link it to a tablet and get all the data...  Works well.

 

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I decline to read this thread because someone has inevitably filled it with math to a point beyond pragmatism. Tempted to scroll up, but I know better.

 

To ensure I’m making powerfactor? Ten is plenty. If I were close? I’d shoot a bunch more to know exactly how close I really am, before going back to the press to adjust.

 

I don’t worry about more than that, unless I’m comparing two loads (like running two powders before choosing one to order cases of) for consistency, and PF, and the like.

 

Edited by MemphisMechanic
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