A very common question on this forum is often along the lines of "Why can't I find a such-and-such recipe using (insert inappropriate powder here)?"
More often than not, the answer is because that particular powder has a burn rate which is unsuited for the application.
So what does that really mean?
There are general rules for selecting a proper powder (in no particular order here):
1. The smaller the bore diameter, the slower the powder required
2. The larger the payload, the slower the powder required
3. The faster the speed, the slower the powder required (and often more of it!)
So it may seem like using slower powder always makes sense, right? Actually no. If you use a powder that is too slow you'll have an inefficient burn with low peak pressure, and you'll need to use much more of it. So you compromise performance and economy.
Need to know what powder speed is best for your load? Generally you can answer this yourself by checking reloading manuals. Look for powders which generate 9,000-10,500psi at the velocity you want and you're usually in the right niche.
Let's use the classic Alliant powders to show the full spectrum:
(From fastest to slowest):
Bullseye - selected light 12ga loads
Red Dot/Promo - 7/8oz to 1 1/8oz 12ga loads under 1250fps
Green Dot - 1 1/8 12ga handicap loads 1250-1300fps, 3/4oz 20ga
Unique - standard payload 20ga and 28ga, 12ga field loads 1250fps+
Herco - 28ga standard payload, heavy field 12ga/20ga
Blue Dot - heaviest 12ga field loads, select 28ga standard payload
2400 - .410
Of course, these are generalities, and there is overlap in some areas, but this gives a pretty good starting point.