I sat down and took a ~30g scoop a went through every powder I have and  made little piles.  I burned each one as I poured it to check and see the burn rate, residue, and just because it's damn fun!

I was absolutely amazed at how much CRAP is left over on some of the powders.  The cleanest powder that I saw was IMR 4198 ... there was absolutely nothing left over, and it left a nice clean yellow stain on the concrete.  Where as Accurate 2230 left a pretty hefty size of residue left over.  On the magnum side; H50BMG was the cleanest burning powder ... Retumbo was also really clean as well ... US869 left the biggest crap pile of all of the powders burned.

Overall it was pretty cool seeing some of the powders putting off a yellow flame, some a red flame, and every others a bluish green.  I tell you what though ... after seeing how much crap some powders left; I will never put quite a few of them down any of my gas driven AR-15s and AR-10s again.  There was so much soot left over by several powders I'm surprised by ARs didn't choke to death.

It was a great experiment though ... I would encourage everyone to check out their powders especially the ones you put in your gas systems.

Not sure it directly equates to how clean they burn in the barrel given the powders burn much cleaner when they are under intense heat and pressure.

Probably not directly, but if one burns more clean than another outside of that environment; it would safe to say that it would burn more clean under that environment as well.  For most guns it wouldn't matter anyway, but any platform that is gas driven it  would effect significantly.  Plus I don't like powders that leave a lot of crude in the cases after being shot either.  I noticed that the 7.62x51 SBS headstamped stuff looks nearly new after being fired ... I would love to know what they are putting in those.

I'll agree with uglygun here. While some powders are inherently more dirty than another, just because they leave some residue when they burn in the open atmosphere does not mean they have the same properties when ignited in a high heat/high pressure environment like during firing a round.

The pressure will not change what residue is left over.  The pressure will just disperse what is left ... basically blowing it out the barrel.  Just take a spoon full of US869 and one of H50BMG .... and you will see what I mean.  I am not talking about performance; speed of burn, or any of those openly debatable questions.  I am simply talking about what is left over when the flame ends.  We all know that some powders leave the inside of your case black while others leave it looking nearly new.  Spend 20 minutes burning a couple different types of powders across the pistol and rifle range and you will begin to understand what I meant.  I have about 18-25 different powders that I keep on-hand and the differences were quite amazing.

For instance; Benchmark leaves a small amount of residue when finished burning.  Instead of your classic yellow flame it is more of a red, and the stain it leaves behind is yellow vs. the normal black stain.  That is why when your shooting .308 rounds loaded with Benchmark they come out looking so clean inside ... the stain it leaves behind is yellow (matching the brass) instead of the black stain that WC846 leaves.

As far as the residue goes .... most left a mound roughly 5-25% the size that we started with after being burned.  US869's residue pile was enormous though .... I would venture to say that it was easily 50% of the total mass that we started with.

One thing we did note was that extruded powders left less unburnt powder.  This would go along with what I have read about ball powder being more difficult to light and not having as a consistent burn rate.

Regardless of the the environment that the powders are burned in; it will not change the chemical compositions of the the powders being burned.  Meaning it will not change the amount of fuel in the powder and how much waste is left over when that fuel is expended.  

And you know this for a fact?




 

I'm no physicist but I do know that as pressure increases temperature also increases. In this case I would think burning powder in open air would leave the most residue.
Those same powders confined in a chamber would burn hotter and burn off more of the residue. So a powder that looks really dirty in an open air burn might not leave as much residue under pressure.

Just sayin'

Yes in a confined chamber the pressure and when temperature increase; the powder will burn more completely.  Pressure will directly affect how evenly the powder burns and help to ensure that it burns completely.  Temperature will affect how much residue is left over though; much like an incinerator.

Regardless; the amount of residue left over will be directly proportionate to the powder used.  If (X) powder is really dirty compared to (Y) powder in the open air ... then even under these changing variables (X) powder will still be more dirty compared to (Y) powder.

The amount of residue will change based on temperature, pressure, amount used, ect... but the amount of residue left behind will remain constant in comparison.  Even if you throw a bag of paper in the incinerator there is still waste left over when the energy the paper stored is burned off.

Putting US869 in a 50BMG case and shooting it will create more residue than putting H50BMG in that same case and firing it.  They will both be exposed to near identical pressures, heat, and physical conditions ... so the result would be the same as if your burning them on the table; not that the residue burned in the case is the exact amount as what is burned on the table, but that one leaves more residue behind than the other.

We all know that some powders are extremely dirty and some are very clean.  Each is the way they are for certain reasons and there is nothing wrong with that.  If a powder that is more dirty produces a good reliable ignition and provides excellent accuracy; then it would be perfect to use in a bolt gun.  The point I was trying to make was that; with some of our guns using the gases to cycle the chamber ... those dirty powders wouldn't be my number one choice anymore because it would affect the reliability of the weapon.  Even Stoner talked about that when he designed the AR platform and the military decided to use a different powder than recommended.  The result was that he had to go back and modify the gas system to function even when those powders were used.

I think you're right but I also think there's more to the equation than meets the eye.

First off, burning is not a simple chemical reaction.  It is a very complex series of reactions which interact with each other.  I believe I remember in high school chemistry my teacher told us that some scientists have identified hundreds of chemical reactions that take place inside the flame of a burning candle.  I couldn't begin to comprehend the reactions that take place inside a bullet as it goes off.

Burned in confinement, byproducts of the burning reaction combine and recombine producing heat and energy in a very short period of time.  But, in open air, those byproducts can escape and heat is not retained in the chamber.  It is very possible that some of the byproducts of burning powder are left behind when not contained inside a bullet as they burn.

I'm not saying you're wrong.  In fact, I think your experiment is a good first step to understanding what goes on when gunpowder burns.
I'm just thinking of what we can do to take this experiment to the next level and see what happens when powder burns in confinement.

Just a "spitball" idea here...
Would it be a fair test to put measured amounts of powder into small, sealed plastic containers like old 35mm film canisters?
I think the powder would burn, the pressure would build and the lids would pop off in a semi-safe manner.  As long as you were a safe distance away and in an area where you couldn't start a fire it would be reasonable safe.  Wouldn't it?
Then you could swab the inside of the containers with a Q-Tip or a piece of white cloth to see what residue is left over.

I don't think this would be a completely true test but I think it might be interesting to compare results with open air burning.

Well ... I have a couple hundred 35mm cannisters that I picked up at the Army Surplus a couple months ago for filling with tannerite.  Now I just need to get some cannon fuse or something to light the powder with the lid closed.  

Another thing is to just load up a 45 ACP round with the 50 BMG powders and shoot it.  Then inspect the case for residue left behind.  The case is large enough to easily look inside ... the slow burning powder will be ok to use in that small of a case because overpressure will not be an issue.  I have an old Rock Island that I can use ... I'll just mount it in a vise and use a string to shoot it .... for safety of course.

Another reasons for looking into this powder/residue thing is ... when I am shooting bursts in my AR there are times that the target gets so obscured by smoke and crap in the air; I have to stop shooting.  It would be nice to figure out which powders are the cleanest burning and then determine out of those; which performs the best.  

An extra note ... Wiedners has some of the Radway Green .308 powder.  All of the RG ammo that I have shot in the past has been some of the cleanest surplus I have used.  Just thought  I would let everyone know it's there.

How about electrical ignition?

Use a piece of electrical cord like an old extension cord with two alligator clips on the ends instead of a plug.  Just clip off the plug and attach a clip to each of the two wires.

Take a thin "cat whisker" of wire and clip it between the clips.  You can get a cat whisker by stripping a piece of stranded extension cord and stripping off all the insulation from a piece 6 inches long.

Put your igniter into the cannister.  Leave a hole for the electrical leads to exit.  Seal them up with a little putty or glue.
Be sure your cat whisker igniter is in good contact with the powder.

Run the other end of the wire to a safe place.  Get behind some cover if you think it's necessary.

Touch both ends of the bare to a battery.  A six volt motorcycle battery or an old car battery should be MORE than enough to make the wire get red hot in just  second or two.  Once it does...  BOOM!

When I was a kid, we used to launch model rockets in my back yard.  The launcher for model rockets is essentially the same as I describe only fancier.
http://www.hobbylinc.com/htm/est/est2230.htm

Once I figured out how it worked, I quit buying stuff from the store and made my own.
Much cheaper and more satisfying because I made it myself instead of buying it from the store.