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Originally Posted by JimBob86
It's been my experience, both with pistol and rifle, that the quicker powders lose less velocity in shorter barrels than the slower ones, though they start with less to lose. There is definitely less flash and bang to them.
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The affect may be so but the cause is the opposite.
Faster powders generate peak pressure sooner and therefor accelerate the bullet earlier. They should reach higher speeds in shorter barrels. But, burning faster means being burnt up faster, obviously, and so those same powders drop off in pressure quicker than do slow powders. The slow powders then "catch up" to the fast ones because the slow powders can generate/maintain pressure longer.
If you start with a really, really short-barrel, the fastest powders should generate the highest speeds. If you start with a really, really long barrel, the slowest powders generate the fastest speeds.
As you cut down that long barrel, the powder than generates the fastest speeds should continue to generate the fastest speeds, to a point. Somewhere along the line, round abouts the length of really long pistol barrel and/or really short rifle barrels, that starts to change, back to the faster powders creating faster speeds.