When the priming compound was changed to the Non-Toxic formula, it was found that the brisance (velocity of the explosion) was much faster than lead styphnate priming compound. This caused the primers to back out of the pockets excessively. The first fix was to enlarge the flash hole, which worked to a certain extent, but when the enlarged flash hole was combined with crimping the primers in place, it worked to keep the NT primers in place.
While this was going on, they also experimented with using small pistol primers in the .45 acp, which was also found to work. This had been done in Europe many years ago, and there were no adverse affects from the use of SP primers. Those companies that decided to use Small Pistol Primers in place of LP primers crimped them in some instances. This was done to make sure there wouldn't be a problem with them backing out, and it works.
Also during this process, they found there were no problems in using larger flash holes with both lead styphnate primers or NT primers, so you'll find .45 acp brass with flash holes that are approximately 1/8" in diameter. These can be from ammunition primed with either primer. I've seen them from Speer, CCI, Federal and Winchester.
