Red Dot vs. Promo - .38 Special

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Morne
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Red Dot vs. Promo - .38 Special

Post by Morne »

Chrony data (all .38 Spl 158-gr CPSWC with COAL around 1.450" with CCI-500 SPP):

3.7-grains Red Dot:
Taurus 617 2" barrel = avg 727 fps; ES 22.8
Taurus 627 4" ported barrel = avg 719 fps; ES 19.4
Taurus 66 6" barrel = avg 695 fps; ES 36.2

3.7-grains Promo:
Taurus 617 2" barrel = avg 733 fps; ES 69
Taurus 627 4" ported barrel = avg 724 fps; ES 84.2
Taurus 66 6" barrel = avg 710 fps; ES 69

Everybody says that you can use Red Dot load data for Promo and the similarity in velocity data supports that. Still, they are most definitely NOT THE SAME. If they were, the ES numbers would've also been similar and they were not. In every case the Red Dot version had a much tighter ES than the Promo version of the load. Is it enough to justify the cost differential? Probably not. I guess I'd rather buy Promo cheaper and live with the sloppier ES than spend more money on Red Dot.
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Re: Red Dot vs. Promo - .38 Special

Post by Sevens »

I'm not sure that in any thread -we- have had (around these parts) that anyone has ever claimed they were the same. Alliant techs are very specific when they direct you that Red Dot published loads can be used for Promo powder.

Also, it might be an interesting experiment to dig deeper in to variances simply in one's technique with the chrono itself. I've heard of (quite!) varying results when folks chrono rifle loads when they willfully alter their physical hold on the rifle. As we might imagine, shooting a rifle from a well-constructed rifle rest on a bench it really is quite easy to hold a rifle either like it's an elephant gun -OR- as if you are barely touching it... and folks (with FAR more hands-on) chronographing experience that I have report quite different results.

My point? Well, I am just left to wonder if the conclusions you've come to here and true and valid, and if the seemingly differing results are as powder related as we may think.

I can also say from experience that crimp and/or case mouth tension ALSO alters chrono results in otherwise same/similar loads.
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Re: Red Dot vs. Promo - .38 Special

Post by evan price »

Red Dot data by weight not volume for Promo. Not the same. I heard from a couple people that Promo is recovered and reground powder from other batches that is reformulated so no two batches of Promo are ever alike. But then again I didn't hear it from Alliant.
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Re: Red Dot vs. Promo - .38 Special

Post by SMMAssociates »

It's been forever, but I used to do non-digital photography, including printing my own enlargements.

When dealing with color printing, a package of printing paper came with calibration data because of variations in the process of coating the paper stock at the factory. When you opened a new box of paper, you used this data in concert with your prior settings to derive new ones for the new batch. Otherwise, green faces & such....

This paper is cranked out (well, was) in quantities that are large enough to make you wonder, but the manufacturers could never standardize the chemical composition between lots sufficiently well enough for all but the most casual users to use it for color prints without doing our own standardization tests. (PITA, BTW. It took me about an hour to "set up" a new paper batch.)

IMHO, the powder people probably don't have as many variables, and probably can manage a batch-to-batch consistency that's much better, but at the end of the day, all kinds of variables are involved, and things like average particle size can cause significant differences in the calibration data that we see. Which means seriously different performance between brands/types. In this case, the velocities are about the same, but things like particle size could seriously effect other things, including accuracy. Just as a trivial example, consider particles popping off at one per second v.s. two per second. The resulting pressures ought to be similar, but the timing has to nudge the projectile a little differently. The more consistent it is, the more consistent we're likely to be when using it. (And, the more cost for the more consistent powder, too. Them guys in the white lab coats cost more :D.)

Velocity and pressure numbers sort of average out by time in the barrel, but a lot can be going on between peaks....

Just IMHO. We now return your discussion to the guys who know what the heck I'm talking about :mrgreen: .

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Re: Red Dot vs. Promo - .38 Special

Post by Whirlwind06 »

So what does ES stand for?
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Morne
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Re: Red Dot vs. Promo - .38 Special

Post by Morne »

Whirlwind06 wrote:So what does ES stand for?
Extreme spread (5-shot string).
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Re: Red Dot vs. Promo - .38 Special

Post by JustaShooter »

Morne wrote:
Whirlwind06 wrote:So what does ES stand for?
Extreme spread (5-shot string).
And for those who are not statisticians, that means the difference between the highest and lowest speeds measured for that string of fire. Generally, the higher this number the less consistent the groups will be.
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Re: Red Dot vs. Promo - .38 Special

Post by Sevens »

And for those who are statisticians... or perhaps better yet -- for those that are scientists, you simply wouldn't put much stock in a data set with only five examples in the test. For ES and especially for SD, you really want MANY.

The better the loads look, the smaller the ES and SD look, the -MORE- examples you (should!) wish to test.

And here merely one reason (of many) that the Chrony brand chronograph that I own, use and loathe... SUCKS. And I will be replacing it one day. The Chrony allows a 10-shot string maximum. And that is a big handful of suck.
I like to swap brass... and I'm looking for .32 H&R Mag, .327 Fed Mag, .380 Auto and 10mm. If you have some and would like to swap for something else, send me a note!
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Re: Red Dot vs. Promo - .38 Special

Post by JustaShooter »

Sevens wrote:The better the loads look, the smaller the ES and SD look, the -MORE- examples you (should!) wish to test.
And that's important - if the ES / SD get big in a small sample, you know you don't need to run a larger sample. But if they are small in a 5 or even 10-shot string, that could just be random chance and you *will* want to use a larger sample to be sure. Of course, a good ES / SD doesn't mean the load will group, and a larger ES / SD doesn't mean it won't, but it is a good indicator.

And here merely one reason (of many) that the Chrony brand chronograph that I own, use and loathe... SUCKS. And I will be replacing it one day. The Chrony allows a 10-shot string maximum. And that is a big handful of suck.[/quote]

Nothing keeping you from combining strings in a spreadsheet - I know, it's a bit of a pain but it's a lot less expensive than a high-end chronograph if that's your biggest problem with the Chrony brand.
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Re: Red Dot vs. Promo - .38 Special

Post by Sevens »

Your argument is sound and I would agree to it -IF- you can assure me that one of the horribly small sample size (five shots here, ten shots for any/all Chrony brand devices) wasn't merely a bad read or some other anomaly of chronograph testing.

As for the spreadsheet idea, certainly works for ES. The formula for SD is far, far beyond that, and light years beyond my mathematical ability. And while it is absolutely possible to make a spreadsheet utilize that formula (and I could even search out that formula and merely cut & paste even without the mathematical understanding of it), the spreadsheet idea will ONLY work if I enter EVERY SHOT in the sample.

I can't make a spreadsheet calculate the true SD if I leave the range only with a result of a 10-shot string (or many of those strings.). The Chrony brand device absolutely has the mathematical ability to do all the work -- but they handicapped it with a 10-shot string limit.

The only thing that I actually find more confounding... is that this limitation seems to bother like NOBODY. But hey, no worries then... I shouldn't have any trouble selling it. The Chrony certainly does a fine job at measuring the speed of a bullet zinging over it. ;)
I like to swap brass... and I'm looking for .32 H&R Mag, .327 Fed Mag, .380 Auto and 10mm. If you have some and would like to swap for something else, send me a note!
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Re: Red Dot vs. Promo - .38 Special

Post by JustaShooter »

Can't you plug the Chrony into a computer and download the data? I was sure they had that ability - that would make it easy to combine the strings. And the SD formula is built-in to every modern spreadsheet program I'm aware of. In Excel it is the STDEV function. See https://support.office.com/en-us/articl ... 650a72c9b0" onclick="window.open(this.href);return false;

(Just got a Chrony for Christmas, planning on getting it out to the range real soon and trying it out and seeing what it is capable of.)
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Re: Red Dot vs. Promo - .38 Special

Post by Sevens »

Bummer. Nope, none of the Chrony brand units will interface with... anything, as far as I know. I believe it's CED that has one out now that will link with my phone via Bluetooth and run in an app. Whichever one that is, that's the one I'd get.

The Chrony has the power to run the Space Shuttle -- as long as you don't mind controlling the space shuttle with THREE single-click pushbuttons and your Space Shuttle never goes higher than 30 feet in the air. :|
I like to swap brass... and I'm looking for .32 H&R Mag, .327 Fed Mag, .380 Auto and 10mm. If you have some and would like to swap for something else, send me a note!
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