You may have run across the Powder Burn Rate Chart (or not):
Faster powder, lighter loads. Slower powder, heavier loads.
Since powder is almost impossible to get, you have to be flexible in your thinking.
For .45 ACP, I use 700-X. It is very fast and a poor choice for newcomers to reloading. A little 'oopsie' goes a long way toward kaboom. It is possible to nearly triple charge the case!
But it's the same story for Bullseye and that is recommended if a lighter load is being considered.
Everybody would recommend a slow powder like Unique. But you might not be able to find any.
Haunt your LGS to see what they have. A pound of powder will almost always make 1000 rounds or so. You can also check out gunbot.net. Here is the link to the powder search:
Basically, gunbot wanders through other web sites looking for inventory.
Here are the two main powder manufacturer's web sites:
I prefer the Hodgdon presentation.