Is there a system or code to the numbers used by the various gunpowder manufacturers?

How can you tell which is a slow powder, which is fast; and, when whould you choose one over the other?

SBT you can find a pretty good explaination in most reloading maunals. The burn rate can vary enough from lot to lot that a definative chart is very hard to produce. I think that the latest Sierra manual has a good chart in it.

Go to the VV website and download the Reloading Manual- the first or second page lists all -or at least a huge chunck of available powders and their relative burning rates.
You really cannot use the relative rates to start reloading by but it does give you an idea of where to look to pick a reasonable powder for your particular application.

quote:

How can you tell which is a slow powder, which is fast; and, when whould you choose one over the other?

By using a powder burning rate chart!

Here's another;
http://www.reloadbench.com/burn.html

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Is there a system or code to the numbers used by the various gunpowder manufacturers?

Yes there is, in a very general sense...The lower the number, the faster burning the powder is.

That is to say Accurate Arms #2 is faster than their #9. And IMR 3031 is faster than their IMR 7828. Also, VihtaVuori N110 is faster burning than their N160.

But it's just a sweeping generality as smokeless gunpowders can burn faster or slower depending on the shape of the cartridge, the weight and construction of bullet,
even the length of the barrel. It is NOT a perfect system.

Manufacturers name or number their canister gunpowders just like auto manufacturers name new models of cars...whatever sounds cool or might catch the buyer's eye. No rhyme or reason behind it at all.

IMR powder numbers don't have anything to do with their burning rates. IMR 4227 is a whole lot faster burning than IMR 3031, for instance. And IMR 5010 is slower burning than IMR 7828.