Interpreting Chrono Results


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Gary H
January 6, 2003, 09:02 PM
Just had my first try at chronographing some ammunition. New CED Millennium and enough sun to make it work provided ten string results for some factory ammo and one reload.

My reload was 45 ACP Shot from a Glock 21

Load: 6.1 gr. Universal
Bullet: 230 gr. West Coast Plated RN
Primer: CCI Large Pistol
OAL: 1.240"

I started with Hornady data for a 230 gr. FMJ-RN / COL: 1.230" / Winchester WLP primers. They show max load for Universal out of a 5" Barrel was 6.4 gr. Resulting velocity was 900 fps.


I used a plated bullet, COL: 1.240 and CCI primers. All parameters that differ from Hornady.

I dropped the charge to 6.1 gr. and loaded on a RCBS Pro 2000.

My chrono results from a ten shot string was as follows:

Ave. Velocity: 917.8
S.D.: 39.2
High: 967.4
Low: 827.0
E.S: 140.4

I didn't see any signs of stress on the brass.

How do I interpret these data?

Does the velocity indicate that I'm in the pressure danger zone?
Is the large standard deviation an indication of poor metering, or is it rapidly increasing pressure with slight changes at, near, or above max pressure? In other words, getting close to overpressure.

I would like to use this as a learning experience. What is a good S.D. for progressive ammo? Is my choice of powder questionable due to metering problems, or is my choice of 6.1 gr. a questionable high starting point?

Thanks,
Gary:uhoh:

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Peter M. Eick
January 6, 2003, 10:15 PM
Quickly scanning the numbers, and compared to my guns, your extreme spread is very large and your SD is high. My interpretation is try another load.

My goal is on a 20 shot string to get the SD below 20 and the extreme spread less then 50. On my better quality guns with careful reloads like my 210-6, I usually get SD's around 10 to 12 and ES's around 30.

Any other thoughts?

mbott
January 7, 2003, 06:05 PM
Gary H,

You might also want to consider trying another primer instead of the CCIs. I will use them in my plinking/blasting loads, but I've decided to quit using them in anything I load for accuracy. I'm seeing just too much variation in my chrony readings and I'm starting to suspect the primers are the cause.

--
Mike

GooseGestapo
January 8, 2003, 08:39 AM
Use Federal or Winchester Large Pistol primers, NOT MAGNUM. Be sure that powder measure stays between 1/3 to 3/4 full- Neither too much nor too little in measure.

I BET THAT YOU'RE USING MIXED BRASS TOO !!!

Seperate all brass into like headstamps. That is the single largest factor in reducing velocity/pressure variations. Best is Federal (for .45acp) Close Second is Starline (IMO), a close Third is Commercial Winchester. All others are relegated to plinking/blasting.

Your 6.0 +/- of Universal is a good load. Just tinker with your components and OAL to find "sweet spot". For really low SD and ES, try either WinSuperTarget or HodTitegroup. Also good are Bullseye and Win231/HP-38.

Myself and all my competition pistol shooting buddies stick with 3.9-4.0 of Bullseye and 185 Star HP or 3.6 and 200gr SWC for 98% of .45acp loading. If these won't do it, load max load of Universal or Unique under a Hornady 185gr HP-XTP. Otherwise, for self-defense either the Hornady factory 185 XTP or Speer GoldDot.

griz
January 8, 2003, 09:45 AM
Like G. G. my first thought was mixed brass. If you try the load with one single lot of brass I would think your results would be better. If the average velocity was still over 900 I think I would back off a bit.

By the way, what kind of data did you get from the factory loads?

Gary H
January 8, 2003, 10:48 AM
Ya, mixed brass..will knock that off.

I haven't chrono'd another pistol load.

I was shooting Q3131A through Rock River NM AR-15 Ave: 3276fps / SD: 28.2

Yugoslavian Surplus 7.62x39 through Yugo SKS Ave: 2411 / SD: 16.2

griz
January 8, 2003, 12:41 PM
Those numbers sound reasonable. Since you said you had clocked other loads I just wanted to make sure you didn't have a chrono problem.

You probably know already but the reason for the wide velocity variation with mixed brass is internal case volume. It varies a lot between different brands.

Good shoot'n, griz

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