You need to be more concerned with bullet-to-case tension rather than crimp! Lead bullets are prone to being sized down during the seating process, a concern that is addressed by controling (i.e."M" die) bullet fit (into the case). Too tight of a crimp can result in bulging the cartridge to the point it will not chamber and it will also, at the very least, result in the bullet being damaged when it is fired, which leads to gas cutting and leading.
●Too much crimp only ruins tension, use ONLY enough to hold bullets under recoil.
●Toughen the bullet to open the crimp and prevent slump and skid.
●Changing the crimp alone does not solve the problems that can be caused when firing opens it. A very light crimp that does not open will still damage a bullet.
Experiment with your crimp. if you can run your finger nail down the finished cartridge and it does not catch on the brass that is enough. If the bullets are not walking forward under recoil that is enough. if they are not being shoved back into the case in a levergun that's enough.
Take a new case, chamfer inside and out, then apply a small bell. Slip the lead bullet in and crimp lightly (into a crimp groove) just so it straightens the case. At this point you should have just a bit of an edge on the case mouth. This is verified by using the cylinder to make sure they will chamber.
If your bullets are moved forward until the cylinder jams, simply push them back in with your thumb, fire them, and then reset the crimp die, screwing it downward another 1/16th to 1/8th of a turn. It only takes a little to tighten the crimp. When the bullet is gripped tighter than tapping with any tool will loosen, (short of banging on it hard), you know it's there for good. Sufficient crimp has been achieved when there is just enough crimp to leave a straight case (from the belling die) and have a bit of an edge that clears everything. Crimp must only be applied at the edge of the case mouth. If the crimp is excessive, it will bulge the brass below it, which is no good and will cause the cartridge to be too big to enter the chamber!