Plan on a couple of "test runs" as you arrive at the best answer for you.
First, fill the case to the point where the bullet will contact, and compress the powder about 1/8 inch or so. Just be sure you're not leaving air space between the bullet and powder. Then, run those loads in a match. If you can hold onto your pistols with that load, you're done.
Second, if you cannot hold onto your pistols with full loads, go ahead and make up some loads with some kind of filler. I like Fluvel, but it's kind of expensive.