The crimp isn't enough to create a pressure spike, at least you shouldn't be crimping that hard. You can get a significant spike if the bullet jams the lands prior to full ignition. I can feel it when I'm shooting. The slight crimp that
@ButterBean recommends just prevents this from happening. Once we figured out what was going on and started using the LCD, the false pressure signs went away and we were able to increase the powder charge till we got to normal consistent pressure signs before backing off and finding a safe, stable load. Since some would jump prematurely into the lands and some would not, we were getting flyers until we started crimping. This pulled everything together remarkably. That was the 124 HH in a CM. Not all of our rifles had the same degree of trouble.