Q about powder speed

[Tom Bri]

I am not a reloader, but am interested in the subject. I hope someone can give me answers to some questions I have about powders.

I know different powders have different speeds. What is being measured exactly? Speed of the expanding gas? Speed of ignition?

How is speed measured? What are the units?

What is the range of powder speeds? I know black powder is very "slow" compared to top end smokeless, but are some smokeless powders as slow as bp?

That is enough questions for one post! Thanks.

 

[Cal4D4]

No expert here, but here's a starter. Forget about rating black powder vs. smokeless. Apples and oranges. I believe Alliant rates their powders as a percentage of the speed of their fastest powder (Bullseye). Speed of reaction is measured under standardized conditions in a pressure "bomb" (test bed). Speed is not linear and many variables can affect it. Characteristics can change as pressure range, temperature and ignition circumstances change. Hope this muddies it up a bit, it really is a fairly complex subject. We just operate in a tiny, well tested range of conditions following an established cookbook.

just for reference...
http://www.handloads.com/misc/burnrate.htm

 

[Mal H]

I agree with all that Cal4D4 said. And to sum up what he said - it all depends on the usage of the powder, or in other words, speed is relative.

If you burn a small amount of smokeless powder outside a cartridge, say a small pile of it in a tin can, you'll see that it burns very slowly. In fact it'll amaze you how slow it does burn. You'll wonder how that stuff can go bang! when inside a casing. It's all in the magical chemistry of the various nitrocellulose compounds used. Under high pressure, NC compounds "burn" a heck of a lot faster.

The terms "slow" and "fast" are hard to relate to when trying to compare something that happens in .002 seconds compared to something that happens in .0005 seconds. Both are extremely fast when compared to our everyday experiences.

The burn rate is changed in several ways. The shape of the individual particles makes the most profound difference. Small thin flat flakes burn quickly as do small balls of powder. Larger thicker flakes or balls are slower, while long tubes (called extruded grains) are even slower. The surface area per unit weight is obviously what is changing as the burn rate goes up. In addition certain additives or coatings on the grains affect the burn rate.

When reloading, it is usually best and always safest to go on the tedious work already done by others. Use the powder recommendations associated with the various calibers you'll find in reloading manuals.

 

[Ktulu]

Actually black powder would be considered fast burning. It produces lower velocity but it burns faster. High velocity is achieved with slow burning powders.

I've never burned any fast burning smokeless powder like really fast shotgun and pistol powders but my guess is that it burns noticeably slower then black powder. Putting a match to a pile of black powder is like putting a match to evaporating gasoline. It's highly volatile.

 

[Archie]

This discussion goes on and on and on...

Very technical question, indeed.

The "speed" of powders is the rate at which it evolves gas (pressure) which is directly related to the rate at which the powder burns. It is very similar to "octane" ratings for gasoline, except I am unaware of any numbers, either absolute or relative, applied to powders.
Don't be confused by powder names like "H-110" or "4350" or "4227". Those are just names and there is no relevance to burn rate.

We all speak in terms of "A is faster than B"; usually that is true in every instance. Every once in a while someone will say something along the lines of "X is twice as fast as Y", but this sort of thing isn't reliable enough to bet the future of a good firearm.

Normally, the speed of the powder is matched to a) bullet weight, b) expansion ratio, and c) desired velocity. As a rough rule:
*A higher bullet weight uses a slower powder, for greatest efficiency.
*A bigger case volume uses a slower powder for greatest velocity.
*A faster powder is used in some loads for lower velocities for target work.
*A faster powder is used in some gas operated weapons to ensure a consistent operational pressure.

As Mal H said, there's been a lot of research done on this by the loading companies already. Don't get cheap on loading manuals. Get several by different companies and read all the introductory material. Lots of good information.

Black powder is a "low explosive". It burns at the same rate whether confined or not.

"Smokeless" (which it is not, by the way) is a progressive combustable. Which is a fancy way of saying the burn rate varies depending on the amount of confinement.

 

[BluesBear]

Which is a fancy way of saying the burn rate varies depending on the amount of confinement.

Which is precisely why one has to be cautious of bullet seating depth and case capacity.

Two bullets of the same weight will create different pressures if the seating depth is different.

Thicker walled military brass often created higher pressures that thinner commercial cases.

These two instances as well as other variables are why you should drop back and then work your way up to where you were when changing ANY component in reloading.

 

[Tom Bri]

Wow. I never realised it was so hit or miss. No units to measure speed. It is all relative to....whatever. I am a little let down.

I am surprised to learn that black powder is "fast" burning. I understood that it is completely different in burn characteristics than smokeless, but was always under the impression that it was generally slow in comparison.

 

[caz223]

Yup, black powder is definately faster burning than your average smokeless powder.

And believe it or not relative burn rate charts compare burning rates to the burning rates of other powders.
There are several relative burning rate charts, and they are helpful in powder selection.
http://www.reloadammo.com/burnrate.htm
http://www.hodgdon.com/data/general/burnratechart.php

 

[30Cal]

Wow. I never realised it was so hit or miss. No units to measure speed. It is all relative to....whatever. I am a little let down.

They run a pressure curve which shows pressure over time, then compair one powder to the next. The one with the earlier peak is faster. Coming up with a unit that means anything would be difficult, and for liability reasons, I doubt anyone would publish that data if they had it.

Ty

 

[Black Snowman]

I am surprised to learn that black powder is "fast" burning. I understood that it is completely different in burn characteristics than smokeless, but was always under the impression that it was generally slow in comparison.

Fast burning relative to most smokeless powders when NOT under pressure. Under operating pressures very few smokeless powders are slower than blackpowder. Blackpowder is considerably more volitile and so ignites easier and burns faster in open air.

If you think you're somewhat frustrated by the strangeness of it think how the scientists studying the field of black magic . . . I mean internal balistics feel. They have a hell of a time predicting anything within an acceptable tolerance even with the horsepower of modern computers. They still have to test everything in the lab. So don't feel bad if it seems a little confusing

 

[Tom Bri]

http://www.americanhandgunner.com/SO03ftr.html

Here is a very amusing picture of what got me asking the questions that started this thread.

 

[caz223]

Large humor!