It'll vary with the bullet choice.
A good rule of thumb is to use the 85% rule, as described in the Precision Shooting Reloading Guide. Fire a round in the brass brand you want to use. A commercial load is just fine. At this point a new bullet should slip into the case mouth, since it has not been resized.
Weigh the fired case and spent primer (still together-this has not yet been resized). Fill the case with water. Stick your bullet choice into the case to the seating depth used for it in the manuals. This will push the excess water out. Now wipe of the outside of the case and weigh it again. Subtract the empty fired case weight from the case + remaining water weight. This is the water capacity of the case under the bullet. Use 85% of that weight as the a charge weight guestimate for your prospective powder.
Now go scan through the load manuals looking for powder charges for that same bullet seated to the same COL at that same charge weight or very close to it. Pick the ones that give highest velocity. Those are good prospective powders, regardless of the final charge weight you land on.
For example:
Suppose you use the Speer SPBT seated to 3.600, as mentioned in Speer's manual. Let's suppose you find the fired case holds 106 grains of water after the bullet has been pushed in to 3.6 COL and the excess water has run out and been wiped off. 85% of 106 grains is 0.85×106 gr. = 90.1 gr.
So you want the powder that gives highest velocity with around 90 grains of charge. Well, the Speer manual suggests that Reloader 22 and Reloader 25 are the two best candidates, with the former having higher peak pressure than the latter (it's a maximum load for Reloader 22, but a starting load for Reloader 25, so, even though Reloader 22 has a little more velocity, being at maximum, there is no guarantee your rifle will get there, and if it does, you've got nowhere further to go. So I'd start with Reloader 25, and work up from 90 grains to find best accuracy.
