If you are having 1 or 2 duds out of a couple hundred rounds, then you need to go back and check that you are feeding your press good components (garbage in=garbage out), that the press is adjusted properly, and most importantly, you as the operator are being smooth and consistent when operating the press.
Usually I can feel or hear when I make a bad round. If, during a reloading cycle, the press just doesn't seem like it should, I pause and take a look at what is going on...is it a high primer, a bad piece of brass, or a bullet issue? Try to fix the ammo before it makes it to the gun.