please explain why mixing powders is bad

When a cartridge is fired you have a controlled explosion inside the cartridge case that pushes the bullet down the barrel. The potential for danger is great. The chemical composition, shape and even coatings of every powder is somewhat different.

Powder and bullet companies spend a lot of time testing different components to develop safe combinations of powder, case, primer and bullet and publish that information in loading manuals. Just a minor change from those specs such as using a different primer, the depth of the bullet seated in the cartridge, a different brand of brass, or a different brand of bullet of the same weight will cause changes in pressure. Even 2 different barrels will produce much different pressures. These minor differences in pressures usually won't lead to a firearm failure, but in rare cases could.

When you mix 2 different powders that have not been tested there is no way to know what will happen when the cartridge is fired. It might be perfectly safe, it might cause an explosion. You wouldn't go into a science lab and randomly start mixing chemicals, why would you do it with gun powder.

Ammo companies do often mix different powders to get desired results. But it is done in a controlled setting and pressure tested to be sure it is safe before ammo is loaded and sold to the public. The data isn't released to the public because it would be impossible for home reloaders to exactly duplicate the mixture.
 
There has been some work on blending powders, going back to development of the .223/5.56. But the final product was with a unitary powder of suitable "burning rate" giving the desired velocity at manageable chamber pressure and gun design port pressure.

The work isn't done in a vacuum (Well, actually, it is.) but I don't know where you would find or get the textbooks the propellant developers work from. I narrowly missed getting a job with Olin/Winchester at St Marks so if things had gone differently 45 years ago I could tell you.

I DID get a little experience with other granular products and can say that a major obstacle to blending gunpowder would be getting a uniform blend and KEEPING a uniform blend. Now if you could make a range of powders of the same grain size but different ballistic properties, it would be easier.

I assume the powder companies do "back mixing" to keep their production lots uniform so as to make cookbook handloading possible. I know other granular products do so, things like fertilizer.

The old time shooters avoided that problem with duplex loading, the different powders carefully kept stratified, NOT blended. The only socially acceptable form of duplex loading is with 5-10% smokeless under black. There are some guys out there working with duplex smokeless/smokeless, but they don't discuss it much in public forums. Too much risk of an Internet Expert jumping in at the deep end and blowing up his gun.
 
I totally 100% get the thing on predictability. Point taken.

The larger issue that I'm trying to understand is modulating burn rate curves. Again, I am NOT a handloader, just a guy who likes to understand *everything*.

I hear talk of "burn rate" and there are even charts comparing burn rates, but what are the units of "burn rate?" I'm skeptical. I expect the propellant burn rate isn't really a single number. What about regressive, neutral, and progressive powders, for example?

I've been surprised to learn that the pressure-vs-time curve for a rifle peaks and drops off so fast, dropping in some cases just barely after the bullet hits the lands if I'm not mistaken. Not that power is the only performance metric, but I had expected that people trying to max out velocity would have tried to keep the pressure up higher for a good fraction of the length of the barrel.

And so naturally I imagined that a combination of "faster" and "slower" powders could get the pressure up high fast and keep it up high.
 
No expert here but powder burn rates are controlled by various techniques. Size or shape of the powder sticks or flakes. Chemistry of the powder itself. Coatings applied to the powder. Some powders even have holes through the sticks to help control burning rates. For the handloader just don't mix powders and follow loading data in manuals.
 
A "burn rate" chart is ordinal and does not have units. All it says is that powder A < B < C. If shown in physical units, say psi of pressure increase per microsecond, C might be 5% faster than B but B 25% faster than A.

Yes, powder is consumed in very short order, most of the bullet acceleration is by expansion of the gas produced before the bullet has travelled very far at all. Progressive powders have spread that out as far as the manufacturers can manage, although there are small improvements from time to time.

One can read of the early experiments of Dick Casull loading .45 Colt brass with triplex charges of Unique, 2400, and Bullseye for a quick launch, steady push, and a kicker late in the burn. Of course .454 shooters now just dump in the H110.

The Germans experimented with what Robert A. Heinlein called a "booster gun" with side chambers up the length of the barrel to keep the fire burning behind the shell. Look up "High Pressure Pump" for an account of the rather poor results.
 
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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One thing I haven't seen mentioned about why its a bad idea to mix or blend powder is that the burn rate /pressure curve of a single powder is affected by the pressure of the burning powder itself.

The powder is made to depend on this. As it burns the pressure rises at a certain rate, which in turn controls the burn rate of the powder. Powder granule shape, size, and chemical coatings ALSO factor in to this.

When you add a different powder into the mix, its different properties will change the total into something UNKNOWN.

it is not a straight math issue. There may even be cascading levels of variable change to the factors over the time of the burn. We don't know how any given combination will react, or if it will be a consistent uniform reaction or a random one in both intensity and direction.

Worst case? as described, a bomb next to your face or at the end of your arm.

Odds of it being a bomb? TOTALLY INCALCUABLE. SO, over all, VERY BAD IDEA.

Could these things be learned by careful experimentation? Possibly. I haven't heard of anyone doing so. If you do, please, let us know!
 
My guess, and that's really all it is, is that it would require too many variables to work to be practical. While it's a very interesting proposition to mix powders to keep pressures high throughout the duration of the fire, but I'm not certain that any action is designed to contain a pulse as high as 20,000 PSI or greater for a period eclipsing a typical peak pressure. In reality, you'd like those pressures to have sloped off considerably by the time the round has exited the barrel and your action is unlocking. Keep in mind, the bullet will exit the barrel within 1ms. Quite generally, handgun powders are fast and rifle powders are slow. Makes sense, right? While you will still see residual burns even past your muzzle, the pressures are safe enough to not hurt you or the gun during it's normal battery cycle. I can certainly see why you wouldn't believe that the results could be catastrophic in all cases, and you might be right when loading pistol calibers with slow rifle powders (don't actually do it, I don't know for sure). However, loading fast powders up into rifle brass will likely be catastrophic and there is a large body of evidence to prove it out there for your research.

So, yeah, it's been done. The reason it isn't done is because it is impractical at best and catastrophic at worst. It's likely that you don't have access to expensive pressure barrels or sophisticated transducers to measure mixed loads. The way I see it, the smart guys have already done the math. Those powders are produced for very specific purposes and to deviate is to invite disaster. It'd be awesome to have someone with knowledge in the industry put in his two cents on why mixing powders is not advised or practiced. I think that the pressure curve and peak pressure time are carefully calculated. I don't believe it's mechanically advisable to stretch that peak pressure time. Somewhere out there is a formula for tensile strength, pressure and time. I hate math so you're on your own.
 
MARCO: He's trolling.... His user name gives him away.

WILL
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I am NOT trolling, my previous joking aside. I only joked about it b/c I was sure that my question would elicit a gut response from people who know you aren't supposed to mix powders, and it was light humor. That's all.

Why?

I'm attempting to understand how to control the pressure curves, by which I mean pressure vs. time.

Look, if you just have instantaneous burn, the pressure is inversely proportional to the distance down the barrel the bullet has traveled. That's not very efficient. If you want to get the highest speed the *mechanical* system (action + barrel) is capable of, you need to have some powder kick in later on down the barrel.

So, why is that such a bad idea?

Barrels aren't manufactured to be safely fired with the full SAAMI pressure all the way from breech to crown, I'm guessing (right?), but I'm also guessing that *most* barrels can handle way more pressure near the crown end than they usually are subjected to, no?

Vihtavuori doesn't even let you into their website until you acknowledge that you shouldn't mix powders. I want to know, what's the danger?

Let me give you a counter example:

I understand that UNDER-loading a cartridge can be very dangerous to your health. I *NEVER* would have guessed that. Why is that? I mean, physically, why is it that under-loading a .30-06 can make it blow up?

To be honest, I'm completely baffled why anybody would NOT want to know the answers to these questions.

Not trolling. But thanks for playing.
 
That's just the point, though. I don't believe that the barrel or action should withstand much more pressure. In reality, they are tested to about 20% more, but you risk compromising the tensile strength. As I pointed out before, the time at peak pressure is a huge consideration. Most actions and barrels will not withstand a longer peak pressure. Also, adding more pressure as your bullet exits means that flames are likely to follow. This would act like a torch on your crown, corroding it and over time degrading accuracy during transitional ballistics considerably.

EDIT: Look into what happens during the firing cycle while the bullet is entering the lands, or leade. That peak pressure is largely responsible for getting the bullet started down the lands after it jumps off the case. Not much more pressure is required to keep the bullet accelerating, and in fact, acceleration increases throughout it's entire travel down the bore. Again, you don't want peak pressures while the action is opening.
 
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Ok. Thanks for the help. I understand that for nearly all handloaders (99.9+%?), the question never even arises, so it's from left field. So I appreciate the answers.

In context, I had thought that a .40 and a 10mm should generate nearly the same energy given that their sectional areas and max pressures are the same (or nearly so). The only difference is case volume.

It turns out that the case volume matters, even though you generally never load the case 100% full. That's an interesting fact, from which I realized (after some reflection) that case volume is important not just for holding powder, but for reducing the peak pressure at ignition - at least for handguns.

That got me thinking about internal ballistics. A lot. So I have lots of questions.... :)

Naturally, when I see big warning signs saying "Don't Do X," my first thought is, "Why?"

I think Jim Watson's story about the .454 Casull was informative. Thanks.
 
It's all been done before, including testing loads to the limits of eventual destruction of the firearm, intentionally.
Like, what would happen if someone loaded their 270 Weatherby with 7mm Weatherby and pulled the trigger? Speer wanted to know and they tried it for us with two rifles so that we would know better. ( The Mauser was destroyed in this experiment, but the Mark V was completely unharmed.)
If you simply must try some of these kinds of stunts, do yourself and everyone who cares about you a simple favor of precaution: Mount the firearm sturdily in an armor plated box from which to fire it remotely. Don't expect to pull such a stunt at an established shooting range; I doubt they would approve. Actually, I don't approve, either. You can probably find YouTube videos of stunts like this gone wrong and people getting hurt. With modern propellants, the wheel has already been perfected. There seems to be no unfilled gaps in the burn rates of so many powders to choose from. We are spoiled for choices. And yet, there are always those who come along and are sure they could do it better. Be safe and don't get in over your head. There are unexpected dangers in the deep water.
 
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I understand that UNDER-loading a cartridge can be very dangerous to your health. I *NEVER* would have guessed that. Why is that? I mean, physically, why is it that under-loading a .30-06 can make it blow up?
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I don't know why you take as Gospel a doubtful, hotly debated and at most an extremely rare phenomenon while at the same time pressing for reasons why the system does not work as you think it should.
 
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?
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Yes, that's the way to do it. You are also correct about the dollars spent. The powder companies spread that cost over the sale of tons of powder. You would have to pay for it up front and get a couple pounds of powder that is perfect for only you. If it were me, I would study the vast literature available about the subject, and instead of buying a pressure testing setup, spend the money on a couple guns, a reloading setup, a chrono, and learn from there. Your choice.
 
Thanks again for the responses.

I meant it as a serious question. Apologies if I came off as being a bit flippant.

So to emphasize: NO I AM NOT MIXING POWDERS and of course neither do I suggest anybody else do it. I was just wondering why it's supposed to be so bad.

Some other dangerous possibilities that occur to me are:

1) grains might segregate or "demix", with one powder near the primer and the other farther away, for example. This makes ignition very unpredictable and it could lead to very high spurious pressures. (Demixing is counter-intuitive but real.)

2) grains of different type might have different surface chemistries that could lead to some kind of flocculation, which again could lead to spurious pressures

3) grain chemistries (stabilizers, etc) might not go well together; in fact, powder A might cause slow degradation (over months) of powder B.

Again, I am not going to do the experiment. I value my health. Just trying to learn this stuff. It's what keeps my brain going.

Like, what causes secondary peak pressures? But that's another topic.

Thanks again,
Regards,
Peter
 
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.
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Well yes mixing powders can do just that . I think you are missing the point and or misunderstanding the burn rates . If a fast burning powder like Win-231 #29 on the burn rate chart and Hodgdon 50 BMG #147 were to be mixed 50-50 in a 50 BMG cartridge it would be catastrophic . Why , because it takes maybe 8 to 10gr of W-231 to get the same pressures as 214gr of H-50BMG . So image what types of pressures you would get loading 107gr of Win-231 into a case when only 8gr is needed to create high pressures .

Now that's on the extreme end of things . Mixing IMR 4895 and 4064 # 90 & 95 on the chart could be done with out blowing your self up but if you mix extremely fast powders with very slow powders you are asking for trouble . Well not asking , You WILL get trouble .

You asked early what books you could get to better understand this topic . A reloading manual would go a long ways in that regard . They don't just give you load data . They have very detailed information as to why what does what in the beginning of all manuals . The Lyman 49th edition is good . ABCs of reloading is another .
 
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you need to have some powder kick in later on down the barrel.
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This is a common misconception even among experienced hand loaders. Regardless of how fast or slow a powder burns it all burns within just a few inches of barrel. A fast powder might need 3-4", a slower powder 4-6". The load that gives you the fastest speed from a 26" barrel will also be the load that gives you the fastest speed from a 16" barrel

The longer barrel will be faster. But is is because the pressure behind the bullet has more time to push on the bullet. The bullet will still continue to accelerate in the barrel long after all the powder has burned. At least within reasonable limits. It is theoretically possible to create a barrel long enough that the bullet could start to slow before exiting, but not with anything commercially available.

Developing loads for short barreled handguns with faster burning powder has some merit. But it is simply not an issue with rifle length barrels.
 
it is not a straight math issue. There may even be cascading levels of variable change to the factors over the time of the burn.
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Thanks for the post 44 AMP. Great information.

Not that I would ever mix propellants. Heck, I don't even mix lot numbers of the same propellant.
 
very simply,you dont know what they will do if mixed together !

unless you have a special lab or something where you can experiment safely not to mention a degree in chemistry.chemicals within chemicals might cross react with each other
 
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