Why not start by loading it as long as possible while still keeping it short enough to cycle through the clips and short enough that the bullet does not touch the lands and grooves in the barrel when chambered? I would establish this as the maximum overall length for use in your gun and clips. Then you can experiment with shorter overall lengths to see if they will improve accuracy.
To work up a load, I would first determine which bullet shoots the best out of your firearm. I would then determine which powder works the best. Then move on to how much powder to use. Finally, I would tinker with the overall lengths to see which shoots the best.
You can check to see if the bullet is touching the lands and grooves by the following method. First, disassemble the pistol. Reload a round and seat the bullet to a length that you estimate is longer than the maximum overall length. Paint the bullet with a felt tip marker and insert it into the dismantled barrel. If it is too long, there should be markings on the bullet where the ink was rubbed off. Next, wipe off the ink with a rag and adjust your seating die down a little further and reseat the bullet a little deeper. Repeat the painting of the bullet with a felt tip marker and check for clearances. Continue this trial and error method until their are no markings on the bullet.
Don't forget to check and see if the bullets will cycle through your clip. With some bullet designs, the clip is the limiting factor.
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