SL1 has one of the problems well covered.
There is another problem, that of leading. Lead bullets properly sized at exactly bore size or a little larger upon firing, swage to fit the rifling and make a good seal. The hot gasses that drive the bullet do not escape past the bullet.
If those hot gasses do get between the bullet and the bore (which happens if you have sized the lead bullet too small) the lead melts and some of it sticks to the bore. You don't want that for a multitude of reasons
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Good luck. Thanks for asking our advice
Lost Sheep