the less you size and dont go under bore size the better.. the cylinder will size after you size, then the bore will size.. the more the bullet is sized the more it can be out of whack.. pros like thier bullet to drop .0005 over bore from the mold and size at that size or right on bore size.. youd do not whan your crimp or neck sizeing to under size your bullet after youve just made it perfect.. load your bullet in a unloaded round then pull it out in press with pliers as you drop the lever down without a die and measure the bullet diameter and see if it is under sized.. for black powder loads pure lead can work very well in .45 colt.. 250 grain hollow base p;ure lead bullts with abut 37 grains 2fg, with measure, was the standard colt .45 factory load. for accuracy make yourself a cleaning kit for your belt and clean between shots for max accuradcy, and then after 6 rounds for general acccuraacy. trim your cases constantly, and soak your cases with a bit of murhy soap oil and water as soon as you can to keep from ruinging them.. different crimp testing is exceptionally important for accuracy.. a littleharder lead like 20-1 or 30-1 and more or less powder may help.. grease cookies, wax checks, bullet lenght, crimp, primer type, and gun quality allhelp.. the heavy recoil with added weight of black powder and heavy bullets ,long barrel time with slow burning powder, and curved grip on the gun make your choice one of the hardest guns to shoot accuratly.. good luck dave.