What is the diameter of the bullet before and after patching? How hard is the bulllet? Is there eveidence of the patch being torn away before the bullet leaves the barrel? Are you crimping the bullet (generally a bad idea), cleaning any sizing lube off of the bullet before patchiing, lubing after patching? How far down the bullet are you placing the patch?
as a general guide, for smokeless loads, your prepatched bullet should be around 0.452", BP less, around 0.449 or so. Give us some more details.