(1) go with what Davemuzz sez. If your sized brass fits the gauge, or the chamber of the barrel, then your problem occurs after sizing and you are probably bulging the case when you crimp. (2) If the cases do not chamber all the way after just sizing, then lower the sizer a bit until you get full length sizing and the cases should drop into the chamber. (3) When you seat the slug and crimp, don't roll crimp the case too tightly - just a slight crimp to hold the bullet in place until you taper crimp using the sizer or a Lee Taper Crimp die.
Lee Factory Crimp dies are good for crimping factory style - a taper crimp. This should work properly for even mixed brass. Another trick you can try in the interim is to take your 45 acp sizer, remove the decapping pin and rod, and run the loaded cases back up through the sizer to remove any bulges. This technique will also work to taper crimp the brass. On occasion you may find a couple of cases that are thin and don't hold the bullet as tightly as others when you crimp using the sizer, and that is when the Lee dies should work better.
I use a old 30-06 sizer to taper crimp my 45 acps. The only time I have a loose slug is when I use mixed brass and with some of those I then use the acp sizer if it tightens things up a bit... HTH.