The problem is that all brass is not created equal. When I started loading I had a nice load for my 45 ACP. Then one time I went to the range and started shooting. The first couple rounds were fine. Then one seemed a little hot. The next one blew out the case, blew the bottom off the magazine and dumped the rest of the rounds on the deck, jammed the slide to the rear and peppered my face with powder and bits of brass. (Thank God for safety glasses.)
Upon examining the rounds that were dumped on the deck I figured out what had happened. The brass cases were slightly thinner that what I had been using. The bullets were not held tightly enough in the case and under recoil had been set back in the cases. Some pistol powders, even with moderate or mild loads can cause soaring pressure spikes if even slightly compressed.
The next day I went out and bought a taper crimp die. I now use a taper crimp die on all rounds that headspace on the case mouth. I seat the bullets in one step and taper crimp them in the next.