I am reminded of a past exchange with William Iorg in which he reminded me that old time bullseye shooters used roll crimps for best accuracy from the .45 ACP in the 1911. The roll crimp actually is the universal one, since it prevents either setback or inertial bullet pull. The taper crimp was popularized solely on the proposition that it extends case life (which it does; I've had up to 50 load out .45 ACP cases taper crimped, while roll crimped mouths often start splitting after just half a dozen reloads). But the accuracy thing is another consideration. A roll crimp increases start pressure more than a taper crimp does. That can improve ignition consistency and velocity consistency, depending on your powder and primer. You need to try both in your particular gun to see what shoots best for you?
Marshal is correct about case growth. It really only happens in cartridges fired at chamber pressure above about 30,000 psi or so. The pressure has to be high enough to stick the brass to the chamber wall against rearward pressure on the head to cause stretching. In lower pressure handgun loads the whole case backs up under pressure, and you often find cases actually shrink slightly with each load cycle from the sizing die flowing the brass back. My .45 ACP target load cases shrink an average of about half a thousandth per load cycle. So, if you identify your shortest .45 Colt case and grind the tip of a Lee trimmer down so you can trim them all to that same length, then load and fire them all the same number of times, you should find the lengths stay pretty well matched.
