Interpreting my first chrono data


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Epicurean
February 26, 2010, 07:03 PM
I finally got my ProChrono running (it appears to be inoperable in not just fluorescent light, but halogen as well) with the addition of the Indoor Lighting Setup. I shot three short strings mainly to confirm my understanding the chrono operations.

First string - eight shots from a cold Sig P239 using Federal 115 grain FMJ to establish a base line.
Average - 1071 fps
ES - 39
Std. Dev. - 12

Second String - eight shots from a warm Sig P239 using my load of 115 grain MBC LRN, 5.0 grains Unique, CCI primer, mixed brass, 1.075" OAL
Average - 1064 fps
ES - 52
Std. Dev. - 18

Third string same as second string except from cold Sig P226
Average - 1117
ES - 89
Std. Dev. 28

This is my first reload in 9mm. There were no failures in any string.

I had hoped and expected that my loads would perform at least as well as Federal range ammo. Alas, no dice.

So here's my questions.

1) How long should a string be to be viable?
2) Is the culprit here the mixed brass, novice loading or both?
3) Should I try to "tweak" this load or try something else? (I have Bullseye and Clays on hand)

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Birdhunter1
February 26, 2010, 07:32 PM
Culprit seems to me to be the mixed brass if you want to get more consistent results you would weight sort your cases.

At least this is what I would do on a rifle, I don't know much about a pistol other than they are lighter, carry easily in a holster and go bang.

Galil5.56
February 26, 2010, 07:34 PM
Not seeing a problem here at all. 3.6" barrel using a 115 gr LRN and 5 gr (metered?) Unique getting the velocity you got and ES seems very reasonable. 5 grains Unique and a Lee 125 grain I cast with that drops about 128 grains, and sized .358" gets 1136 fps avg from my 5" Beretta and ProCrono Digital. Had I run this same load over my Shooting Chrony Master F1, it would have read close to 1200 fps.

Although I shoot very little lead that weighs 115 grains, personally to give you some perspective, maybe the next time you purchase powder try one that has a pressure curve on the more rapid side... Say WW231 or similar. Although the efficiency is a bit on the low side using more Unique, you have a bit more room to work up if desired to exceed the Federal velocity safely. Nothing wrong with Unique at all, just that it takes so little relative pressure to drive a 115 LRN, that I would be inclined to go with somthing a bit "quicker" if given a choice.

1SOW
February 27, 2010, 01:39 AM
I load 9mm and use 10rds for testing, 8 should work. I throw out a 'flyer' that's way outside the norm range (for whatever reason). They do the same at a 'Match' chronoing for power factor.

In 9mm, mixed cases will affect it some, but not that much if you're using Win, PPU, R&P, F.C., etc. --- standard brand cases. Some presses will make a difference with mixed brass. 9mm is more sensitive to oal and charge weight than bigger cases. I sort cases because I'm anal, use a turret press and can 'feel' the difference between some cases (thinner, thicker, softer-whatever) when reloading. Bullet lengths can vary considerably.

9mm (small case) likes fast powder to be 'flexible'. Bullseye, Win 231/HP38, Vhit n320, etc. I know someone who uses 'Blue Dot' , and it shoots fine, but it isn't flexible at all. What you get is what you get.

mongoose33
February 27, 2010, 09:14 AM
Could be anything--are your OALs the same? What kind of bullet are you using? Are the bullets consistent or do they vary from one to the next?

Others have mentioned the brass, which might also influence results. You also may have inconsistent powder drops (how accurate were you with it?).

Also, how far from the chrono were you shooting? You'd want to be at least 5 feet.

You should be able to beat commercial ammo in consistency and quality, so that's your goal.

When I am working up a load, I have a final "production" load in mind. Say I'm starting at 4.0 grains of "XYZ" powder, and the max or accuracy load in a reloading manual is, say, 5.0 grains.

I'll load 5 rounds at 4.0 grains; these are "proof of concept" rounds that I'll shoot through the chronograph just to ensure I'm where I thought I should be. I'll look for pressure issues, but velocity will tell me something about that. Then I'll load another 5 rounds at 4.2, probably 5 rounds at 4.4, then 15 or 20 rounds at 4.6, 4.8, and 5.0 grains.

I'll shoot 5 rounds of each load batch (sometimes there are only 5) to evaluate the velocity and keep track of how velocity is rising as I increase the powder load. If I have a lot of rounds in that batch, I'll shoot 10 through the chono to create a good data string.

With the loads I have larger batches for, after the 5 rounds (sometimes 10 if it's a load I think might be a good one) are shot through the chrono, I'll take the last 10 and do accuracy shooting with them. That way I have a measure of their velocity and consistency, and also assess their accuracy.


There's a rule of thumb for rifle consistency that suggests your SD (Standard Deviation) should be less than 1 percent of the velocity. When you can do that, you're producing some pretty consistent ammo (it may or may not shoot as accurately as the next load out of your rifle, but that's a different deal).

For handgun ammo, I've never heard of a similar rule; what I've learned is that it's difficult to get the standard deviation under 1 percent given the mixed brass I load. Generally, I consider that if I'm under 2 percent SD, that's pretty decent. I've never used new handgun brass and tried to control all the variables, but I'm sure that with more consistent components I'd do better.

[hmmm....I have some new Starline brass in .45; I should see what I can do with that....]

I'd evaluate your second string of shots as not bad; the third string less so.


Finally: One must be careful in interpreting statistics like these. One or two bad shots can greatly influence the overall result. As 1SOW says, a flyer doesn't necessarily invalidate the load. You could have 8 rounds like this: 1152, 1141, 1163, 1155, 1147, 1160, 1153, 1097; that last round is not consistent with the rest, will greatly expand the ES or extreme spread, and will inflate the SD or Standard Deviation.

If I produced the above string, I'd say that my load can be expected to produce around 1150fps; I'd acknowledge the outlier of 1097, and continue to work to reduce the variability of such outliers.

Galil5.56
February 27, 2010, 10:22 AM
I had hoped and expected that my loads would perform at least as well as Federal range ammo. Alas, no dice.

So how was the accuracy of your ammo? I have shot a ton of my ammo that had extremely small SD/ES that were not as accurate as ammo that had numbers 3x as "bad"... Lots more to accurate ammo than how small you can get ES's/SD's within reason, how reasonable is up to your own testing.

jfh
February 27, 2010, 11:23 AM
1) How long should a string be to be viable?
2) Is the culprit here the mixed brass, novice loading or both?
3) Should I try to "tweak" this load or try something else? (I have Bullseye and Clays on hand).

ANSWERS:

1. To begin to have statistical validity--e.g, probability at the 90+% level for repetition--a string has to be a minimum of 10 shots.

2. Yes, the culprit is both probably mixed brass and novice 'problems.'

However, this is a well-done reload, you did as good as can likely be done. It is not uncommon with handguns to have broader EDs and higher SDs. Based on my experience, this seems to be a function of case capacity and modern, low-volume powders. However, the numbers from chrono testing are only additional info, not the goal. Find the load that is the best combination of feel, function, and accuracy that is closest to you desired velocity--and shoot it. Period.

3. Sure you can tweak the load--I'd start with common headstamp brass, and then trim it all. But, unless you are planning on bullseye competition with this pistol, I wouldn't bother with those techniques save for common-headstamp sorting. You can play with LOAs and crimp, but if the load feels good, those are mostly activities designed to fulfill mental masturbation.

Jim H.

Walkalong
February 27, 2010, 11:25 AM
Not seeing a problem here at all.Me either. Like Galil5.56 asked, is it accurate?

=========================================================

Three examples. Shot 2-07 at 48 Degrees. Mixed brass. All accurate.

Ranier 115 Gr RN 5.5 Grs N330.

16" barreled CX4 Storm

Avg 1360 FPS ES=28 & SD=8

3" barreled EMP

Avg 1058 ES=74 & SD=23

-----------------------------------------------------------------

Ranier 115 Gr RN 7.0 Grs AA #5.

16" barreled CX4 Storm

Avg 1430 FPS Es=22 & SD=7

3" barreled EMP

Avg 1109 ES=68 & SD=19

------------------------------------------------------------------

Ranier 115 Gr RN 5.7 Grs WSF.

16" barreled CX4 Storm

Avg 1385 FPS ES=30 & SD=10

3" barreled EMP

Avg 1090 ES=73 & SD=22

=========================================================

Another example. Shot 8-08 at 96 Degrees

Ranier 115 Gr RN 4.5 Grs N320. Mixed brass. Very accurate, very soft.

16" barreled Sub-2000

Avg 1253 FPS ES=67 & SD=24

4 1/2" barreled TZ 75

Avg 1115 ES=20 & SD=7

3" barreled EMP

Avg 1043 ES=32 & SD=10

These are not load suggestions. Check manuals and use at your own risk.

You can play with LOAs and crimp, but if the load feels good, those are mostly activities designed to fulfill mental masturbation.Couldn't agree more.

Epicurean
February 27, 2010, 11:39 AM
Here's how I got to this load. I initially loaded 25 rounds with 3.0 grains of Clays and had one stovepipe in my P226 so I decided (perhaps prematurely) to try another powder. I loaded 25 rounds with Unique and function tested with no failures. I then loaded 100 rounds with Unique for chrono testing in various guns. I am using a Lee LCT so the powder was dispensed using an Auto Disk. I checked every tenth load and was within 0.1 grains of powder and OAL varied more than I wanted; +/- .004 inches.

I was not testing as much for accuracy as I was for chrono operation and understanding. The Federal factory ammo did group a little better however. Feel and function were more than satisfactory.

I like Unique. It seems to burn cleaner than Bullseye and Clays. It also has more volume to it which allows a much easier visual charge check and it would be impossible to double charge. It is a slower burn than the others and that may be my problem.

Now that I've got the chrono working I might try test loads with all three powders to see which is more consistent. When I do this should I sort brass, trickle powder and have no variance in OAL to make it a fair test?

P.S. Mental masturbation is the name of my game!

Walkalong
February 27, 2010, 11:47 AM
Yea. Reloaders tend to like to beat things to death. :D

Clays is mighty fast for 9MM, especially plated or jacketed. Not that it could not be used.

I could not fall in love with Unique and the 9MM. I much preferred AA #5, and shot that for years, lead and plated. Recently I tried WSF, and I really like it in 9mm with plated and jacketed bullets. Haven't tried it with lead. N330 is awesome, but pricey. N320 is awesome for light loads, but AA #2 comes close, and I like 700X for light 9mm loads as well.

(No pun intended. I just re-read my first line)

jfh
February 27, 2010, 11:49 AM
"...When I do this should I sort brass, trickle powder and have no variance in OAL to make it a fair test?"

Well, sure. I assume you know enough of The Scientific Method (here, change one variable at a time) to know technique is the only way you can find the factors that go into your goal.

But, there's a bigger picture--here, that includes the firearm you're shooting. If you are looking for self-education, chase the variables. Doing that is a good exercise for any novice reloader. But, in the long run, unless you are shooting a Sig P210 or any custom-built racegun, you will want to home in on a load that you shoot reliably and not agonize over.

added on edit: I really like WSF, Walkalong, in general. In your shooting, look for leade leading--maybe. I'm doing more testing this year with it.

Jim H.

Walkalong
February 27, 2010, 11:52 AM
I have been told it is good with lead, but I have not tried it.

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