please explain why mixing powders is bad

M

mrentropy

New member
I am not into handloading but I would like to learn.

I have heard that it's a very bad idea to mix powders. So far I have never encountered an explanation why.

Can anybody explain?

While we're at it, I'm looking for a good technical book on the subject. So far the only book I've found so far that really treats internal ballistics in any depth is this one, from the looks of it:

http://www.amazon.com/dp/1466564377/ref=rdr_ext_tmb

I'd like to understand more about powders in particular. Chemistry, physics of making progressive burn by changing powder grain geometry, etc.

You bandleaders are always talking about this or that powder load & cartridge combination, like some black art (no offense - just maybe a little tiny trolling, but totally innocent I swear). Really, what makes a load accurate, when you get down to it?

Thanks.
 
Because a given powder has a specific consistent burn rate and pressure curve. Mixing powders removes that.

What problem are you having that you think mixing powders is a solution to?

And didn't you post this same question a couple days ago?
 
I have heard that it's a very bad idea to mix powders. So far I have never encountered an explanation why.
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It's a "really bad idea" because it is not a prudent thing to do from a safety standpoint. But there's no voodoo involved. It's not like you're going to accidentally make a plutonium bomb. The mixed product will be just that: a mixture. It won't be greater or less than the sum of its parts. But by mixing powder, you will have a completely untested product, with no data for it.

Handloading ammunition can have severe consequences when not done properly and the elimination of variables is paramount for safety. By mixing powders, a huge variable is created. Thus, it's just not a good idea.

Really, what makes a load accurate, when you get down to it?
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Usually, the bullet. Now I only load for handguns, so it may be (probably is) different in the rifle world. That said, it's been my experience that the bullet itself is the most important variable for accuracy.
 
Because all powders are not created equal. If you just throw a bunch of leftovers together, even if they were somehow compatible, it would be impossible to recreate that blend consistently. It could also be quite dangerous. Sugar is no substitute for salt, even though they look similar. Accuracy is built upon following a consistent recipe. Reloading; it's not for everyone.
 
I think you need to explain what you mean by "mixing powders"; perhaps that is where the big confusion lies. For example, let's say that you have a can of powder A and another can of different powder B. Now it kind of sounds like you are asking can powder A be mixed with powder B to come up with an entirely different powder C and then use it to load cartridge XYZ. The answer of course is no since there is no loading data worked up for that powder combination and I really don't think you are meaning that.

On the other hand you should be asking something like why can powder A be used to load cartridge XYZ while powder B should not be used. Then you will be heading in the right direction. You'll quickly find out that a variety of powders, depending to some extent on bullet weight being used, can be used for cartridge XYZ while other powders cannot. All of that will be apparent in loading manuals. So if you mean can more than one (rather than using the term mixing) powder be used by itself for cartridge XYZ, the answer is yes as long as you go by the manual recipes. So kindly reword your query so everyone knows what you are asking. Use of the term mixing powders is perhaps the confusing factor.
 
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Because a given powder has a specific consistent burn rate and pressure curve. Mixing powders removes that.

What problem are you having that you think mixing powders is a solution to?

And didn't you post this same question a couple days ago?
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Yes, I did ask the same question but I thought it vanished into the ether. I don't see it.

Just trying to understand, that is all.

Say I have powder A with its pressure curve. And powder B with its pressure curve. To what extent is the pressure curve of A + B equal to the weighted average of the two curves taken separately?

I'm also trying to understand what is dangerous vs what is just benignly crazy.
 
Since the subject of "pressure curves" comes up:

I haven't heard of these, but I'm assuming it's pressure vs. time taken in a fixed-volume confined chamber, read out with a piezo. (Or are they taken in actual rifles?)

The term itself kinda suggests that burn rate vs. time is an inherent property of the powder grains, and that it's more or less independent of other variables such as the chamber temperature and pressure themselves.

If that is true, then each powder will have its own curve, which is a function of that powder's grain chemistry and geometry. Which means that by combining two powders A + B, you are given *far* more control over the overall shape of the pressure vs time curve then if you had to just stick to one powder.

That's the idea. It hinges on the idea that the burn rate of a "powder" is not a collective effect, but is really set by the burn rate of individual grains, and that that in turn is something that once set in motion, just does what it does independent of everything else. I don't know how good or bad of an assumption that is.
 
I'm also trying to understand what is dangerous vs what is just benignly crazy.
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Firearms cartridges operate in a somewhat narrow window of safe pressures. If you stuff a case with powder that burns too fast for the bullet to leave the case before to the pressures reach levels that cause the case to rupture you have essentially taken the step from firearms cartridge to small pipebomb.

A small pipebomb that will either explode right in front of your face (in case of a rifle) or at arms length (if a pistol).

This being the case, propellant and projectile manufacturers take great care to establish what powder/case/projectile combinations are safe in order to stay on the right side of the pressure limits.

If you take two or more powders with different burn profiles, or even similar burn profiles, and mix them together there is no way of telling what would result in a safe load other than to experiment. Most people involved with handloading would consider such experimentation dangerous.
 
If you take two or more powders with different burn profiles, or even similar burn profiles, and mix them together there is no way of telling what would result in a safe load other than to experiment. Most people involved with handloading would consider such experimentation dangerous.
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That makes sense.

So why not use a really, really solid action & barrel, with a remote cable trigger, and put a piezo pressure sensor in the chamber (and maybe a few in the barrel too) with ns readout and a computerized data acquisition system, stand very far away, and get actual pressure readings?

Obviously that's a lot of work and $$$, but that would be the way to do it wouldn't it?
 
Say I have powder A with its pressure curve. And powder B with its pressure curve. To what extent is the pressure curve of A + B equal to the weighted average of the two curves taken separately?
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There is really no way of knowing, aside from coming up with a "mixture" and testing it, preferably in a pressure barrel. Even then, the mixture will probably never be 100% mixed, and some samples could have more or less of one of the powders, causing erratic pressures.

It is really not a good idea, and is a solution to a non problem. There are so many different powders available, there is no reason to try and concoct some special "mix", when whatever goal you are trying to reach (assuming it is realistic) can always be met with an off the shelf powder with published load data.
 
Mixing powders is kinda like the guy I saw on You Tube, trying to tell people how to reload .40 SW. He had loose primers in a glass jar and more loose primer lying on the reloading table. He was asking for trouble. I refused to watch any more of his so called instruction video.
 
So why not use a really, really solid action & barrel, with a remote cable trigger, and put a piezo pressure sensor in the chamber (and maybe a few in the barrel too) with ns readout and a computerized data acquisition system, stand very far away, and get actual pressure readings?
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To what purpose? What are you looking to achieve by mixing powders that is so important that you would go through the trouble described above as opposed to using a single powder with well published load data?
 
Thanks for the help.

And no, I'm not mixing powders anytime soon. I'm not even reloading - yet.

But it's my nature to analyze the crud out of everything I do. And I study hydrodynamics for a living, so I'm a bit interested in the topic from that angle as well.

For example, I understand that an underloaded round can blow up. I *believe* this may be due to aerosolized particulates in the round undergoing detonation instead of deflagration. Now, that can be bad. It can kill you.

So from what I understand so far, mixing powders is mainly bad b/c you don't really know what the pressure is going to do, which could obviously be very bad and could hurt you, but not quite in the same league as a detonation in which the pressure can peak to 10x or more of the nominal pressure.
 
There are so many powders out there for every popular and semi-popular cartridge that mixing powders seems like an odd proposition. If you want a powder with a specific burn rate you should probably just go buy a powder that would work.
A better question would be - Why would you ever think it necessary to mix powders?
 
Actually, I think the testing is being done. It appears to me that powders are a complex pellet formulation, often coated and sized with graphite(guess) and other stuff thrown in. Some even have multiple pellet sizes.

If mixing were better, powder companies would do it.

In the end, they are trying to make a pellet that meters well, burns controllably, builds pressure in a narrow spectrum and delivers repeatable performance with flexibility for the hand loader to "develop" specific loads.

Mixing takes this known entity and creates unpredictable results. The unpredictability comes from 2 pellet formulas that increase burn rate non linearly with pressure. Then you add a different component which will be effecting each others burn rate...nothing reasonably predictable here.

Test chambers are just simply very thick walled barrels with sensors and bulletproof actions.
 
Some powder information if you want to know details about certain powders.
http://www.ilrc.ucf.edu/powders/index.php
Click the "search database" in the top menu. Scroll down past the list of parameters and then click the blue link "sample detail and download" below each powder. Shows pics of granules, chemistry, etc. Very interesting even for the long time reloaders. The pictures of the powder is 10X resolution. Check it out.
 
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