Reloading manuals by powder manufacturors often provide loading data of several powders for a given combination of caliber and bulletweight.
If one has accuracy in mind, what type of powder is the best choice then? slower or faster burning?

I've usually had better luck with the powder that used the most capacity without requiring a lot of compression. Seems like I get more uniform ignition.

Not in any way intended as a putdown, but honestly, the question has no meaning except with regard to one specific rifle at a time. There really is no general comparison possible here.

If one has accuracy in mind, then one had best be mindful that every rifle is different. To find any given rifle's most accurate load, one has to try the entire range of powders and bullets that are usable for it until you find a load that meets your standards. You won't (hopefully) have to test every one, but you will likely have to test a lot of them.

There is no magic table that will tell you what will work best, even generally speaking. You can pull two rifles off of the rack identical in model and chambering with consecutive serial numbers and it is unlikely that they will shoot their very best with the same powder and bullet combination. They might both shoot the same loads well, but each will have different preferences for its optimum load. I'm not talking about "minute of deer" hunting accuracy here, but rather about finding out what a rifle is truly capable of and the particular load that will realize this. There are a lot of good "general" loads for a specific chambering that will perform decently in many rifles, and these loads are sometimes a good place to start looking, but the reason there are a bunch of powders listed with a range of burning rates is because there are plenty of rifles that find their optimum load at one end or the other.

It's not unusual to have to load and shoot four or five hundred rounds to test each bullet weight with the range of appropriate powders, then another few hundred to find which brand or style in that weight shoots best. Then playing with different primers, then differing OAL's. I think of each rifle as a puzzle to be solved. Sometimes I hit on a great load very quickly, other times it can take weeks or even months. Hobbies are supposed to keep you occupied, after all.

I use the powder that gives me the most combustion with the greatest load density. This eliminates the powder positioning variable and I can concentrate on primers, OAL and such.

That's a good point, Ralph.
While I agree that the greatest possible loading density is preferable for a number of very good reasons, it is not always a route to the most accurate load. Often I find best accuracy in the middle of the range of charge weights for a given powder. Given a choice between two loads using two different powders that produce the same group size, I would also choose the one that fills the case better, but that's not always an option.

There is no right answer.The only way to determine which will be the most accurate n your gun with your chosen bullet is by trial and error.Sometimes it will be the faster powder,and sometimes it will be the slower powder.

Load books have some suggested powders.
The data is usually inaccurate [low charges and high velocities] and biased toward slow powders.

Are those powders the base line of the question?

quote:

Originally posted by ramrod340:
I've usually had better luck with the powder that used the most capacity without requiring a lot of compression. Seems like I get more uniform ignition.

After over 40 years of reloading, that's also my experience. Occasionally, a "faster" powder that leaves a lot of space in the case will provide excellent accuracy (most often the case with centerfire .22's), but more often I'm happier with a powder that completely fills the case, preferably with just a little compression.