This is an interesting topic that I'm glad was started. Here's where I got the notion of the primer moving the bullet first but I guess maybe I've misinterpreted what was said. This is by Allan Jones of CCI, printed in the Sept issue of Shooting Times entitled "Mysteries And Misconceptions Of The All Important Primer" from the section "Too Much Primer": "You can have too much primer.When the output gas volume of the primer approaches that of the cartridge case, sometimes special handling is required. I remember when CCI was working with some experimental primers for 9mm Luger, and we started seeing odd time-pressure curves on the computer. Instead of the normal single peak, we saw two. One QA tech commented that it looked like the dual humps of a Bactrian camel. It was a classic case of high gas volume but too little temperature. The primer's extra gas unseated the bullet while still trying to light off the main charge, producing one peak. Then the bullet retarded as it engaged the rifling, creating the second peak. Although a shooter would never notice this in a production firearm, that double hump was worrisome and we abandoned that mix" The article goes on but that was the part that caught my eye. Interesting huh? This gets me wondering about really light charges of "somewhat" slow powders, eg Unique, HS-6 etc, in large cases like the .45 Colt. (Guess that's why there are "starting" loads!)....Anyway, FWIW, Dennis