The crown! the crown! ------- Loading tight combinations is all about the condition of the crown. Without a smoothly crowned muzzle, loading accurate tight loads is next to impossible without damaging the patch. The patch must not be damaged as it is being loaded or when guiding the ball out the muzzle.
Turn the gun periodically, to assure an even crown. I run a clean patch or swatch of cloth down a couple inches to catch the 'dust' of the emery or wet/dry paper, then after crowning, pull that out with needlenosed plyers, carefully.
To re-crown your muzzle, stick the end of your thumb into the muzzle hard with the emery or paper under it and rotate your hand, bakc and forth, back and forth, rotating your rifle or smoothbore as noted. In 15 minutes, you can have a perfectly smooth, polished crown. Use 320grit for 'roughing' and up to 600 for finishing, although the finer grits arent necessary.
A lathe makes this a 20 second job after running the barrel through the headstock and tightening the chuck.
I've NEVER achieved anything remotely connected with good accuracy using a patch of less than .015" & with that patch, a ball that was .0025" LARGER than the bore was necessary.