Steps to get the perfect bullet for your gun!
1. Get a bore cast of your bore at the muzzle use cero cast if you can, if not you can shove an oversized lead soft cast bullet through the bore. Normally .001 bigger than that measurement is what works but not always. So get the size bullet you measured, and one size bigger bullet and one size smaller bullet.
2. You load them with your favorite load to see what one shoots the tightest group.
Shoot off a benched sandbag at the very least.
If you can do it indoors, or on a windless day and be sure your not shooting close to tall grass or weeds, hitting the tips of weeds, and even getting close with your bullets. If you do your testing will give you no results at all. If you do not have perfect conditions don't bother doing the testing, be very fussy about this.
Clean the barrel in between each group for lead, until you get the right size and hardness you can get quick leading and all testing after that happens will be worthless. I use a piece of copper chore boy over a patch with solvent. How ever you do it, clean it well in between each series of test, then shoot at least 1 or 2 fouling shots with the bullet your going to test with. The first shots after cleaning will often go wide and wild (even if its only wide by .5 inches it screws up your testing.
3. When once you have determined what sizing shoots the tightest, then try the best two (2) sizes in the harder cast with the same load to compare it to. From that test you can determine what size and what hardness you should use.
Remember if the softer cast bullet shoots best then great, but watch for leading if it leads go to the harder cast.
Normally if it shoots good with one powder the same bullet will be the one that shoots good with any other powder. So if you want to try other powders and primer combos later to tighten it up further it will not be a problem and you don't have to do this all over again.